Traffic signals are dynamic signs or sound emitters which display or broadcast traffic commands, particularly at intersections. They usually take the form of lights which change color according to the command, but they can also be on/off single-color lights, mechanical flags or wheels, or speakers issuing beeps, clicks, recorded commands, or other sounds.

The displayed or audible command changes to direct traffic. The device can use mechanical movement or sound as well as colored lights.

A directional sign indicates a route to a destination. A traffic signal issues commands about traffic movement, and need not be a conventional three-light road signal.