It’s time again to dispel a modern mystery that lurks in plain sight. For previous columns, click here; to submit your own suggestions, see the e-mail address below.

It’s time again to dispel a modern mystery that lurks (conveniently) in plain sight. For previous columns, click here; to submit your own suggestions, see the e-mail address below. What do Clerks, a great many Simpsons episodes and Season 2, Episode 6 of Breaking Bad have in common? The convenience store. There are nearly 150,000 convenience stores in the United States—in other words, one for every 2,000 of us, roughly speaking. Total spending at these stores—about $682 billion in 2011, or around $2,200 per person—is greater than the GDP of Sweden. Or Saudi Arabia—perhaps a more apt comparison, given that convenience stores mostly sell petroleum. (Gasoline comprises about 70 percent of convenience store sales.) At many convenience stores, including every 7-Eleven in the United States, there’s a strip by the door with lines that mark out height in feet. Height strips, as they’re known, appear in many retail, banking and fast-food environments, in addition to convenience stores. What are they for? As always a few guesses:

What do Clerks, a great many Simpsons episodes and Season 2, Episode 6 of Breaking Bad have in common? The convenience store.

There are nearly 150,000 convenience stores in the United States—one for every 2,000 of us, roughly speaking. Total spending at these stores—about $682 billion in 2011, or around $2,200 per person—is greater than the GDP of Sweden. Or Saudi Arabia—perhaps a more apt comparison, given that convenience stores mostly sell petroleum. (Gasoline comprises about 70 percent of total sales.)

At many convenience stores, including every 7-Eleven in the United States, there’s a strip by the door with lines that mark out height in feet. Height strips, it turns out, appear in many retail environments. But what are they for? As always a few guesses:

a) Door-height assessment: For those delivering inventory, the height strip is a quick reminder of the vertical clearance.

b) Eyewitness help: Height strips were developed to help eyewitnesses gauge the height of a fleeing robber.

c) Evidence gathering: Height strips came along after the spread of surveillance cameras, and allow those cameras to capture the height of fleeing robbers.

d) Crime deterrence: The strips don’t often help the cops solve crimes, but they do serve as a psychological deterrent. They are meant to be noticed, so that potential criminals will see them and think twice.

And the answer is…

b). I suspect this one wasn’t too hard: With their abundant locations, late hours, wide range of products, high cash turnover and often just one clerk on duty, the popular image of convenience stores is as bullet-riddled as Apu, the proprietor of Kwik-E-Mart on The Simpsons. (“Here’s a pointer, try to take it on the shoulder.”).

What’s surprising though, is that while height strips were first deployed to help clerks or customers gauge the height of fleeing criminals, their function today is largely psychological deterrence.

A little history: Back in the mid 1970s, studies were undertaken by the Western Behavioral Sciences Institute and Dr. Rosemary Erickson, a leading forensic sociologist, to determine how convenience stores could lower their robbery rates. A series of recommendations included time-controlled safes, limited cash-on-hand, lighting that was not only bright but carefully balanced between indoors and outdoors, and unobstructed lines of sight from outside the store. (The latter is usually achieved by moving the cashier closer to the entrance, and by removing merchandise and posters that block the view into the store. Another good reason cashiers have moved toward the middle or front of stores: As more stores started selling gasoline, clerks needed to be able to activate the pumps—and shut them off in an emergency.)

7-Eleven was the first chain to adopt these recommendations nationally. Later, the National Association of Convenience Stores offered a package of these measures to all its members. For good reason: These measures are remarkably effective. Convenience-store crime rates fell by 50 percent between 1976 and 1986.

Height strips predate such programs, but their widespread deployment came as a result of them. And both happened long before the deployment of video cameras. Rollie Trayte, a security consultant and former police officer with 25 years of experience in convenience-retailing crime prevention, says the plan was that clerks would note the heights of robbers as they fled their stores. “The original idea was that cashiers should be trained to be good witnesses—and not resist or fight with robbers. Treat them like your best customer: give ’em what they want and get ’em out the door.” Dr. Erickson adds another reason height strips were deemed necessary: Clerks, when giving descriptions to the police, frequently overestimated the height of criminals. Anyone can look tall when they’re pointing a gun at you.

Today, though, consultants like Dr. Erickson actually advise clerks—and customers—not to use height strips to clock the heights of criminals. One reason: surveillance cameras will capture not only a criminal’s height but often a good image of their face, if it isn’t concealed. The more important reason, though, is that she doesn’t want robbers to “see the clerk, or customer, trying to identify them.” Witnesses “can get shot for that,” she says.

So why keep height strips at all? These days the purpose of height strips is mostly psychological. And their target is both customers and robbers. Convenience store owners want their stores to look safe and welcoming to customers at all hours, and height markers—along with good lighting and security cameras—are meant to signal that the store and the chain take safety seriously. Apparently, the opposite possibility—that anti-crime measures will suggest that a store and its customers have something to worry about—isn’t a great concern. Perhaps we’ve gotten used to cameras, or have come to view crime as an ever-present possibility.

Experts say that unlike cameras, the Psy-Ops impact of height strips on regular customers is limited, because few customers notice them, and fewer still consider their purpose. But criminals, they say, do notice them. To a potential stick-up artist, height strips have come to indicate the presence of the entire array of successful anti-crime measures developed for convenience stores over the last few decades. A store that deploys height strips signals that it is taking security seriously. A robber might well decide to take his or her business elsewhere.

Such signaling, though, is open to abuse: Dr. Erickson notes that some businesses simply display height strips without bothering to employ the other essential parts of the anti-crime program, giving “the false impression that they are conscientious.” (Batesian mimicry, anyone?)

There’s another surprising dimension to the psychological impact of height strips. When else might you see one? When you’re being booked by the police, or standing in a police line-up. Chris McGoey, a security consultant in Arizona who was a height-strip pioneer in the 1970s, says it was common for criminals to report that height markers “made them flash back to the last time they stood in a police line-up, or while being photographed before being booked into jail.” In fact, among all the ways a height strip might deter criminals, McGoey ranks this “flashback effect” as the most important.

Rollie Trayte told me that in his decades working on convenience-store safety, he regularly received calls from law enforcement agencies asking them to send over retail-style height strips. Which means that in a convenience store criminals may well encounter exactly the same height strip design that they stood in front of the last time they were arrested.

Not many of us regularly rob convenience stores, but there are other ways a trip to the convenience store can lead to a police station. Drunk driving, for example, is often precded by a booze run at a convenience store. The height strip on the way out, if we notice it, could serve as a reminder of how little we want to see another one at the end of the night.

If you see something out there you’re wondering about, take a picture and send it to whatisthat@markvr.com. For now, “Thank you, come again!”

Previously in What’s That Thing?

Wall Socket Buttons

Elevator Button

Pastoral Doodad

Ominous Gizmo

Dashboard Arrow

Mysterious Wires

