You might notice if you're ever in New York waiting for a subway train: When the car comes in, conductors always point at a black and white sign hanging in the center of the platform. It's the law, designed to ensure that the train is far enough inside the station and fully in line with the platform. Only after they point can the conductors open the doors. This holds true across all 468 stations.
So two YouTubers positioned themselves under the black and white signs