What is a Signal?

• A. A colored banner outside the depot.
• B. A mechanical switch only.
• C. A whistle used for warning.
• D. A method or device conveying visual and/or audible information affecting movement of a train, rail car, or other on-track equipment.

Answer: (D)

A signal is any method or device that communicates information to trains or on‑track equipment that changes how they move. It uses visual and/or audible cues to tell the operator what to do—stop, proceed, or adjust speed. That’s why the option describing a method or device conveying visual and/or audible information affecting movement best fits. The other items aren’t signals: a colored banner outside a depot isn’t used to control movement; a mechanical switch changes the track route but isn’t signaling; a whistle warns but doesn’t convey movement instructions.