Which of the following actions should not be taken when handling a Call for Orders signal?

Relying solely on the Automatic Train Control (ATC) system when handling a Call for Orders signal is not prudent because it eliminates the necessary human oversight and decision-making crucial in ensuring safety and compliance with operating protocols. The ATC system, while helpful in many scenarios, may not account for all situational variables that a trained human operator would recognize. Proper response to a Call for Orders signal involves awareness of context, communication with relevant personnel, and often, the ability to adjust to changing circumstances that systems alone may not address.

In contrast to this approach, stopping the train as required, notifying the Trainmaster if there is uncertainty, and proceeding with caution are all actions that enhance safety and operational integrity. These actions involve critical thinking and communication, which are vital when navigating potentially complex situations in train operations.