What does a calling on signal look like?

A calling on signal is specifically designed to convey to train drivers that they may proceed cautiously despite a potentially restrictive signal ahead. In the context of railway signaling, a red signal aspect indicates that the train must stop, but when accompanied by a red marker light, it indicates that the driver is permitted to proceed past this signal at a reduced speed, ensuring that they remain vigilant for any potential hazards.

The use of the red marker light is crucial as it differentiates this special instruction from standard red signals that typically mean a complete stop without any further action allowed. This combination effectively informs the train driver that further proceeding is sanctioned, albeit with the required caution.

Understanding this can help in recognizing that other signal combinations, such as green, yellow, or flashing aspects, denote different meanings and operational protocols that do not provide the same instructions as a calling on signal.