Why do we say "traffic signal" NOT "traffic sign" for traffic light?

Question

Why do we say "traffic signal" NOT "traffic sign" for traffic light?

Answer 1

Traffic signals send encoded information that  "signal" you to do different things at various times (eg; stop, go, etc...). A traffic sign is a constant warning or notification that never changes.

A traffic light changes but a stop sign does not.

Answer 2

cause a sign is on a post in the ground not hanging from a wire in the middle of the street

Answer 3

Traffic signal or light changes and lets you know when and when not to go.  A traffic sign says only one thingand stays the same.