Those who signal - (the clue is in the name).
Can be both the equivalent rank to Pte in the Royal Signals or another soldier trained to use a radio or carrier pigeon.
Use of semaphore is not common except when the modified form is used to make your displeasure know to inconsiderate drivers, although no flags are involved.
Despite this, the sign of a qualified siggy is a badge in the shape of a pair of crossed flags. Hence the nickname flaggy. Or brewbitch, but that has nowt to do with flags.
Incidentally, the only military trade I ever achieved was Signaller Cl 1.