When New Yorkers are waiting to board a train, most of their energy is focused on elbowing their way into the car as fast as possible. But if they were to take their time, they might notice something peculiar: after pulling into the station, a subway conductor will always point his or her finger out the window. This isn't something conductors do for fun or out of superstition: The repetitive gesture is a safety precaution, and when you follow their finger you'll see they're always pointing at the same thing.

Halfway down every subway platform in New York City there's a black-and-white-striped bar of wood that's hung in a very important spot. When this indication board, or "zebra board," is lined up perfectly with the conductor's window, that tells them it's safe to open the doors. Any further back and the rear of the train could be stuck in the tunnel—same goes for the front end if it stops too far past the board.

Because opening the doors without a platform to step onto is such a serious concern, conductors are required to point at the sign every time to show that they've stopped at the right spot. Four years ago, an MTA conductor explained the procedure in a Reddit AMA:

"They don't trust us to just look, so required procedure is to point to it at every station before we open the doors. The absolute biggest violation a conductor can make is opening the doors where there isn't a platform. If that ever happens, the first thing supervision is going to ask you is 'Did you point to the board?'"

Zebra boards first began appearing in subway stations around World War I. In earlier systems, one conductor was positioned between every two cars to operate their doors individually. New technology made it possible to open all the doors on a train at once, and the MTA switched to having one conductor in the center of each train. The striped boards have been used as a handy reference point ever since, but it wasn't until 1996 that the MTA began requiring conductors to point at them.

This rule didn't originate in New York, but on the other side of the globe in Japan. Japanese train conductors use pointing to acknowledge many different factors throughout the journey, including speed indicators and upcoming wayside signals. But when you see conductors making the motion in New York, they're almost always pointing to the same object. As the pranksters in the video below discovered a few years ago, this level of consistency can be exploited to have some goofy fun.

All images courtesy of YouTube.