What does a calling on signal authorize a train to do?

A calling on signal is specifically used to instruct a train to move past a signal that is displaying a stop aspect, but do so at restricted speed. This means that while the train is not permitted to proceed at normal speed, it can continue its journey with caution, usually in situations where track is clear and the train can safely move forward. Restricted speed ensures that the driver can stop within the distance visible ahead, allowing for any unexpected obstacles or conditions that may arise.

The other options represent actions that are not applicable to a calling on signal. For instance, proceeding at normal speed would not be safe if a stop signal is being disregarded, and stopping until further notice or reducing speed without a clear directive does not align with the specific authority granted by a calling on signal. Such signals help maintain safety protocols while allowing movement in controlled scenarios, reinforcing the importance of understanding operational signals in train management.