definition
strict definition
ship traffic signal
Signals displaying or broadcasting changing commands to ships, boats, and other waterborne traffic.
Ship traffic signals are lights, mechanical flags, audio speakers, or other forms of signage which display or broadcast dynamically changing commands to waterborne traffic, especially ships and boats.
The command is intended for vessels on the water. Lights, mechanical indicators, and audible signals are alternative forms.
A fixed route indicator gives continuing guidance, while this signal changes its command. A vehicle traffic signal controls road traffic instead of vessels.