All New York City subway platforms have a black and white striped sign mounted facing the tracks. When the subway conductors, who ride in the middle of the train rather than the front, see the sign, it means that the train has pulled far enough into the station for all the cars to be aligned with the platform.
An official and silly MTA rule says that conductors must point at the board as an extra gesture to acknowledge that the train is stopped at the proper location on the platform. One Youtube commenter who appears to be a conductor said
Conductors point at the board because it is required by TA rule. This idea was adapted by the Japanese subway in the mid 90's. We point because if the window of your cab is somewhere within limits of that board, it means the Train operator, the one who actually moves the train, has stopped at his/her mark for the correct number of cars the train has. We also have to point because supervision does move around in the field and yes they actually WATCH us to make sure we comply with this rule. If we don't, well then its not going to be a good day at work...
After learning of this ridiculous rule, Yosef Lerner and friends made comedic signs a la "point here if you [INSERT FUNNY THING]" and stood underneath the signs to grab some smiles from the normally stoic conductors.
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