Which of the following must be displayed on the trailing end of the rear car of the train?

The requirement for a marker of the prescribed type to be displayed on the trailing end of the rear car of a train is crucial for ensuring safety and visibility. Markers serve several purposes: they help identify the end of the train to other railroad personnel and equipment, provide important information regarding the train's status, and facilitate safe operations, especially in low visibility conditions.

Markers can include lights that are typically positioned on the rear car to be seen from a distance, indicating the presence of a train and its direction. This helps prevent accidents, as other trains and vehicles can better determine how far a train extends on the tracks, making it essential for operational safety.

While headlights, reflected signals, and fog lights are important for various situations, they are not specifically mandated to be displayed on the trailing end of the rear car. The marker fulfills a specific regulatory requirement and plays a critical role in the safety protocol of train operations, making it the correct answer.