What is indicated by the 'Doors to Open' signal?

The 'Doors to Open' signal specifically indicates which doors on the train are allowed to open for passengers. This signal is crucial for ensuring safe and efficient boarding and alighting procedures. It helps to mitigate confusion among passengers, as it clearly designates the active doors for access. This is particularly important in busy transit environments where multiple doors may be available, but only certain ones are operational or safe to use at a given time.

In contrast, other options relate to different operational signals. The signal for passengers to board typically does not just indicate which doors can be opened, but rather a broader context of the boarding process. Similarly, readiness for departure signifies that the train is about to leave, while completion of a station stop pertains to how the train has finished its pause at a station. Thus, the 'Doors to Open' signal serves a specific and critical function that focuses on enabling access to the train at designated points.