What does a blue signal signify in train operations?

A blue signal is an essential visual communication tool in train operations, specifically indicating that workmen are on, under, or between rolling equipment. This signal is crucial for ensuring the safety of maintenance crews or workers in potentially dangerous situations where they may be in close proximity to moving trains or equipment.

When a blue signal is displayed, it ensures that any train personnel, including engineers and conductors, understand that the area is active with workers, thereby obliging them to take necessary precautions. It typically mandates that the equipment in question cannot be moved until the signal is removed, ensuring that the workers have a safe environment to perform their duties.

Other options, while they relate to train operations, do not accurately represent the purpose of the blue signal.