Then there are the choices candidates make in presenting themselves to a prospective employer: Whether short or tall, black or white, male or female, one needs to decide whether to wear a suit or jeans, or to show up clean-cut or shaggy, or, like Torres, covered in tattoos. On a resume one can choose to offer up one’s undergraduate GPA, and mention that it was from an Ivy League institution, or one can avoid saying much of anything about one’s education at all.

It could be argued that lots of these aren’t exactly choices: Harvard chooses its students, not the other way around. Acing advanced calculus is similarly something that is out of reach for many, so not everyone can be a math major with a 4.0 GPA.

That’s correct, sort of. But it can also be thought of this way: The cost of adding a credential to a resume or presenting oneself in a particular way at an interview is higher for some applicants than for others. In a sense, the “cost” for many of getting into Harvard and making it to graduation is infinite—it’s just not within the realm of possibility. For a math whiz or a music prodigy, it may not be that difficult to get in and coast through whatever the Harvard curriculum might throw at them. A driven, conscientious, and reasonably bright young person might also put together a Harvard-worthy college application without too much trouble, relatively speaking.

In Spence’s model, the same attributes that make it relatively easy to get a Harvard degree—math wizardry, drive, diligence—are also characteristics that make for a productive employee. If that’s the case, then companies will do well to hire Harvard math majors, even if it turns out that no one learns anything of practical use, or even any math, at Harvard.

Why? Because a math degree from Harvard is seen as a credible way of telling companies, “I’m smart.” In contrast to just saying to a recruiter, “I’m smart,” a Harvard math degree is not something that less able applicants can mimic, or would even want to, because the cost—in terms of work hours and psychic suffering—is too great for those lacking high-powered analytical skills.

Stripped down to its essentials, Spence’s signaling model simply requires that there be a link between being productive, honest, good—anything that’s a desirable, yet hidden (at least from the buyer) attribute—and the cost of doing something. And that something can be anything, really, as long as everyone knows it’s cheap for the smart and virtuous to do it.

It’s easy to think of an Ivy League degree as a useful signal and why people would want to get one if they could. Less so for Roberto Torres’s San Fer gang tattoo, even though it’s doing much the same job as the Harvard degree. What makes it hard for most people to think of a prominent tattoo in this way is that they’re focused on the awful cost of having to go through life with dimmed employment prospects and possibly even a crosshairs on their chest.