signalman

Noun

A signalman using semaphore for "M"

(countable) A signalman is a person who works on the railway and changes the railway signals.
The signalman changed the light from red to green to let the train continue.
(countable) A signalman is a sailor who sends signals from the ship.
The signalman waved his semaphore flags to send a message to the admiral's ship.