A call-on signal is used only in conjunction with which type of signal?

A call-on signal is specifically utilized in conjunction with a home signal to provide specific instruction to train operators in situations where a train may need to proceed past a signal that is displaying a stop indication. Home signals are used at the entrance of a block, and when a call-on signal is illuminated alongside a home signal, it indicates that the train can proceed with caution into the block even though the home signal is not displaying a clear aspect.

The presence of a call-on signal enhances safety by allowing the operator to move the train into a potentially occupied block while acknowledging that the signal indicates a limit to the train's movement due to a stop condition. This functionality is critical in complex operations, especially in yard areas or during specific maneuvers where train movements must be closely monitored and controlled.

In contrast, block signals serve to inform operators about the status of the blocks further down the line, while advance signals provide information about the upcoming block conditions, and clear signals indicate that the track is clear for a train to proceed without restriction. However, these signal types do not have the same function or relationship with call-on signals as home signals do.