What device is mounted on a fixed support to convey messages for regulating, warning, or guiding traffic?

The device that is mounted on a fixed support to convey messages for regulating, warning, or guiding traffic is a traffic sign. Traffic signs serve several vital functions, such as providing instructions or warnings to drivers, indicating roadway conditions, and enhancing safety by guiding traffic directional flow. They are permanent fixtures along roads and highways, ensuring that drivers have constant access to essential information regarding speed limits, road hazards, and other critical traffic regulations.

While other options like traffic lights and signal beacons also play important roles in traffic management, they tend to involve more dynamic regulation of traffic flow rather than simply conveying messages in a static manner. Road markings, though effective for guidance, do not have the same visibility and are not mounted signs, which further distinguishes traffic signs as the correct choice in this context.