What does an illuminated indication light signify for a train operator?

An illuminated indication light signifies that all side doors are closed. In train operations, this is a crucial safety feature. When the doors are fully closed and secured, the train is indicating that it is safe for departure and that passengers are not in danger of being caught in the doors. This ensures that the train can operate without risk to individuals on board or on the platform.

Understanding this aspect is vital for a train operator, as it directly relates to the safety protocols and the operational readiness of the train. Ensuring that the doors are closed before departure helps to prevent accidents and ensures a smooth and safe journey for all passengers. The other scenarios represented by the other options highlight different safety or operational checks but do not pertain to the function of the indication light clearly signaling closed doors.