One of these will be found in every station, near the center of the platform, or wherever the conductor's position falls when the train is properly positioned at the platform. The numbers on the board correspond to the number of cars in the train. So, in this example the board is for a 6-car train. The conductor of a 10-car train would likely not pay it any attention since his 10-car board would be farther up the platform. The idea is to center the train closest to the main stairway, which is usually in the center of the platform. If the train stops with the conductor's position short of or beyond the proper board corresponding to his/her train, the conductor will know that the train operator has pulled up short, or overrun the end of the platform. In either case, there is the possibility that one or more doors would open where there is no platform, endangering unwary passengers. With this indication, the conductor can tell the train operator to pull up if he stopped short, or disable the doors in the first car for passenger safety (train operators are not allowed to back up under these circumstances).
