What must the engineer communicate upon observing a distant signal with a yellow disc marked "D"?

When the engineer observes a distant signal displaying a yellow disc marked "D," it is essential for them to communicate both the name of the aspect and the track number in multiple track territory. This procedure is crucial because it ensures that all crew members are aware of the signal's indication and the specific track they need to focus on, particularly in an area where multiple tracks are present.

This communication enhances safety by confirming the engineer's understanding of the signal information and clarifies the context for the crew, facilitating appropriate actions to be taken as they approach the signal. Additionally, confirming the track number is vital in preventing any miscommunication that could lead to unsafe situations, especially in busy areas with more than one track.