How must the Dispatcher ensure proper delivery of a Form D before a signal to proceed is displayed?

To ensure proper delivery of a Form D before a signal to proceed is displayed, it is essential that the Dispatcher confirms the Form D is delivered beforehand. This practice is crucial for maintaining safety and compliance with operating procedures. The Form D is a critical piece of information that relays important directives and condition updates related to train operations, including specific instructions that the crew must follow.

Ensuring that the Form D is delivered prior to a signal being displayed helps prevent potential confusion or unsafe situations that could arise if the crew receives crucial information after the signal has allowed them to proceed. This proactive measure supports effective communication and proper adherence to train operation protocols.

The other options, while related to communication and updates, do not specifically address the priority of delivering the Form D before signaling the crew to proceed, making them less applicable to the requirement that all necessary information must be received correctly and in advance.