IN THE mid-1990s a man named Frank, recently released from prison, came to Gregory Boyle, a Jesuit priest in Los Angeles, for help. Frank was having a difficult time finding a job, in part because of his chequered past. It probably wasn’t helping that he had the words “FUCK THE WORLD” inked across his forehead.

Father Boyle hired Frank to work at a bakery he had set up to provide jobs to people trying to go straight. He also found a doctor to help remove his act of nihilistic rebellion from his face. The bakery was the first business in what is now Homeboy Industries, a non-profit which has since grown to be America’s largest gang-rehabilitation centre, offering employment and other services to hundreds of former gang members. Its free tattoo-removal service has become the organisation’s biggest claim to fame.

Such programmes are spreading all across America. Half a mile from Homeboy, at the Twin Towers correctional facility, a Los Angeles County jail, inmates on good behaviour are eligible to have their tattoos removed free of charge while still incarcerated. The process is painful—one ex-convict describes it as being hit by a rubber band that’s on fire—and can take multiple sessions stretching over months. But many decide that changing the personal yet public messages written on their skin makes the pain worth facing.

Talking to the prisoners reveals that sometimes it is the personal that matters most. When asked what suddenly spurred him to want to erase the name of an ex-girlfriend, Edward Marron at Twin Towers responded matter-of-factly that his “baby’s mom didn’t like it”. (On his left arm the name of another ex-girlfriend is almost but not entirely obscured by a cover-up tattoo of a tree.) Some just resent the shoddy craftsmanship of their prison ink—one inmate wants to have his Pittsburgh Steelers tattoo removed so it could be redrawn by a professional.

However, tattoo removal can be a more meaningful endeavour: zapping away an old tattoo can change how others see you. When those others are judges, or prospective employers, that can be good; when they are erstwhile gang-mates, it can carry risks. Perhaps most important, removing your tattoos can also change how you see yourself.

The personal is statistical

Individuals choose to write stuff on their bodies—or erase it—because of what that specific tattoo means to them. But the prevalence of tattooing in America’s prison population means that, in principle, it should be possible to formulate general rules about what people say on their bodies, too—to add a statistical meaning to the tattoo’s biographical, or simply graphical, one. The Economist decided to investigate what inferences about a life of crime it might be possible to draw from different types, and numbers, of tattoos.

The websites of many state prisons feature public, searchable databases of their inmates. The data usually include their names, height, weight, demographics, criminal histories, and, sometimes, whether or not they have any distinguishing marks, including tattoos. The most impressive of these, for our purposes, was that of the Florida Department of Corrections (FDOC): a downloadable database featuring records for all the 100,000 inmates currently incarcerated in the Florida state prison system. It provides a great deal of detail on their markings as well as their ethnicity, age and crimes. With a few lines of code it is possible to discover what tattoos a particular Florida inmate has, and where on their body they are located.

The most obvious thing these data show is just how common tattoos are. Our tabulations of the data show that three-quarters of the Florida prison population has at least one tattoo; the median inmate has three. The data also confirm how generational criminal tattoos are: a whopping 85% of prisoners under 35 have tattoos compared with 43% for prisoners aged 55 and over. In the public at large the rate is 23%. The majority of these tattoos have no explicit associations with the criminal world. The most popular designs and motifs include names, animals, mythical creatures (dragons and unicorns are especially voguish) and Christian symbols such as crosses, rosary beads and scrolls with verses from scripture.

The database shows relatively few inmates with overtly criminal tattoos. For example, 15% of white inmates had heart tattoos, while just 3% had tattoos relating to the white-supremacist movement. Some tattoos reflect remorse: at least 117 inmates have tattoos with variations of the phrase “Mother tried”. Thirty-one Florida inmates appear to be big fans of the hip-hop group NWA, sporting “Fuck the police” tattoos. Some tattoos are humorous: at least seven inmates have the words “Your name” tattooed on their penises.

Different demographic groups opt for very different tattoos. Unsurprisingly, white inmates are more likely to feature images associated with the white-supremacist movement: swastikas, Iron Crosses and the like. Hispanic inmates, often raised in Catholic households, favour Christian imagery: the Virgin Mary is a common subject. Black inmates prefer words, eg “Precious”, and often carry slogans relating to gang life. Female inmates are more likely to carry tattoos of butterflies, hearts and the reminder that “This too shall pass” (“Boss bitch” isn’t often seen on men, either). Male inmates are more likely to have tattoos of images directly relating to incarceration such as prison bars and guard towers.

If people’s ethnicity and sex determines their tattoos, can the same be said of their types of crime? Using data from the FDOC, The Economist built a series of statistical models to predict the likelihood criminals had committed particular crimes based on their demographic traits and choices of tattoos (see table).

Our analysis finds that inmates convicted of property crimes and weapons-possession offences have the most tattoos, while sex offenders, particularly those convicted of paedophilia, tend to have the fewest. Inmates with at least one tattoo were actually 9% less likely to have been incarcerated for murder than those without. The effect is even more pronounced for those with tattoos on the head or face, who are around 30% less likely to be murderers. Similar associations can be found for perpetrators of domestic crimes. Those relationships hold even after controlling for age, race and sex.

Some prison-specific motifs are also more common among the less violent. These include tattoos of clocks without hands, prison walls and spider webs, all reflecting the tedium of incarceration, and a popular tattoo depicting the thespian masks of comedy and tragedy along with the slogan “Laugh now, cry later”. Such tattoos are positively associated with low-level offences, but negatively associated with homicide.

Inmates with Christian tattoos—that is, those inked with images or passages from scripture—do seem to be slightly more virtuous. They are 10% less likely to be murderers than those without (this result holds regardless of any difference in types of crime committed between Hispanic and other prisoners). But though the godly may be slightly more good, the devilish are not obviously more evil; tattoos featuring pentagrams or images of Satan are not statistically significant predictors of homicidal tendencies.

Kevin Waters, a criminologist at Northern Michigan University and former Drug Enforcement Administration agent, notes that understanding which tattoos are purely aesthetic and which are signals can be a lot of help to law enforcement, distinguishing truly hardened criminals from posers—gang members do not take kindly to outsiders adopting their imagery. What can tattoos more directly associated with criminality tell us about an inmate?

A common Florida prison tattoo, predominantly seen on Hispanics, features three dots between the thumb and index finger. The tattoo is shorthand for mi vida loca, or “my crazy life”, and its wearers are 45% more likely to have been jailed for murder. Members of the Latin Kings, the largest gang in Florida, often sport tattoos of a five-pointed crown or the letters “ALKN”, which stands for “Almighty Latin King Nation”. Our analysis shows that inmates bearing such tattoos are especially dangerous—they are 89% more likely to be killers.

The truth in black and grey

Nazi imagery is the most obvious characteristic of white prison gangs, but they also favour classically European images ranging from four-leafed clovers to the Valknut, a Viking symbol comprised of three interlocking triangles. Perhaps because of their ubiquity, white-supremacist imagery is not as predictive of murder charges as some other tattoos—still, we find that inmates bearing such symbols were 19% more likely to be murderers.

Picking up on your cellmate’s record from his skin is doubtless a useful skill for those inside. Policymakers, though, may care more about what tattoos say about the future than what they reveal about the past. Nearly half of inmates released from federal prisons and placed under supervision, and three-quarters of those from state prisons, are rearrested within five years of release. Demographics serve as depressingly effective predictors of recidivism. At the federal level, eight years after release, men are 43% more likely to be taken back under arrest than women; African-Americans are 42% more likely than whites, and high-school dropouts are three times more likely to be rearrested than college graduates.

How do tattoos fit in the picture? In a study published in 2013 Mr Waters, along with fellow researchers William Bales and Thomas Blomberg, looked at the link between recidivism and the presence of tattoos in Florida prisoners. They found that after controlling for demographics and crimes committed, inmates with tattoos were 42% more likely to be re-incarcerated for committing a violent crime. A subsequent study by Kaitlyn Harger, now of Florida Gulf Coast University, found that upon release, ex-cons with tattoos could be expected to last just 2.4 years outside prison before being re-incarcerated, compared with 5.8 years for those without. The effect was especially pronounced for those with tattoos on the hands and face. Our own analysis of Florida prison data corroborates previous research. We find that of the 60,000 first-term prisoners released between 1998 and 2002, 45% have since landed themselves back in prison. Tattoos are unreasonably effective predictors of recidivism: we find that of the inmates who have been re-incarcerated, 75% percent had tattoos. Just 30% of the former convicts who have managed to stay out of prison were noted as having tattoos. Gang life looks notably hard to escape. Eighty-one per cent of those recorded with Latin Kings tattoos were rearrested at least once after their initial release. Predictive as they may be, it would be hard and probably foolish to argue that the tattoos cause the recidivism; far more likely that both reflect something else about character and circumstance. Similarly, tattoo-removal programmes seem unlikely in and of themselves to make anyone an intrinsically better person. But they can reflect a genuine investment in change (remember those burning rubber bands) and they may also help reduce the amount of discrimination reformed ex-cons face. As tattoos permeate the mainstream, though, being ink-free may mean less and less. Attitudes towards tattoos are liberalising: in a study that the Pew Research Centre, a think-tank, released in 2010 38% of Americans aged 18-29 had tattoos, compared with 15% for those aged 46-64. Indeed, an intriguing example of their mainstreaming can be seen in the influence of Californian prison gangs on tattoo culture at large.

Tattooing behind bars is prohibited. This does not come close to stopping it; but it does mean inmates must be creative when it comes to art supplies. One constraint is ink, which often has to be improvised from materials like boot polish or the soot from burned textiles—say, cotton. Such sources limit artists to monochromatic tattoos.

Finding the right tools can be challenging too, as hand-poking a tattoo on one point at a time can be both laborious and painful. A breakthrough came in the 1970s when inmates in California discovered how to create improvised tattoo guns using the motors from cassette players. The new gadgets made tattooing behind bars quicker, but featured only a single needle, which made drawing thick lines more difficult.

These constraints, along with the aesthetic sensibilities of Hispanic prison gangs, led to an entirely new style of tattoo—the “black and grey”. The style’s thin lines and colourless palette was put to the service of more realistic imagery than Americans had previously been accustomed to. The style quickly spread to prisons in other states—and then to the outside world.

Freddy Negrete, one of the original pioneers of the black and grey when an inmate (and the originator of the “Laugh now, cry later” motif), notes that initially, people on the outside got the tattoos so as to look as if they had been in prison. But he suspects that the hipsters and celebrities he now tattoos in the same style at his parlour on Sunset Boulevard know nothing of the style’s origin.

Nor, it seems likely, would most of them feel comfortable around the gang members from whom their style of tattoo is derived. Walking through the doors of Homeboy Industries is a jarring experience for those who have no previous experience of a life of crime beyond the occasional speeding violation: the dozens of former convicts decorated with images of skulls and Aztec warriors in the lobby look pretty forbidding. Some are inked from head to toe. Very few are keen on eye contact.

But walking through those doors for job advice, for a tattoo removal, or for any sort of help can be just as difficult. The staff, many of them former convicts themselves, are eager to help, but the criminal life is not one which fosters trust in others. Many former convicts have too much pride to ask for help. Others are convinced that they can never reform themselves. But for those who can muster up the courage, removing the marks of a prison tattoo can be the ultimate act of rebellion.