One of the unique features of airmen serving a wireless trade, is that they wear a badge on the sleeve of their uniform, to signify their belonging to any of the several radio and radar trades. Consensus of opinion suggests that originally these were worn by signalers. Up until 1918, ordinary ranks could not address an officer without first speaking to an NCO. Through the first World War, for the first time, this was often found obstructive when many things were happening at once. Consider that the first world war was the first war to simultaneously utilize no less than three armed forces in the same war. Fast effective and efficient correspondence was necessary to co-ordinate their efforts. A signaler wishing to pass on vital information then, had first to pass it on to the corporal, who then passed it to a sergeant, from whom it was given to the relevant officer, a clumsy arrangement and fraught with problems if the message was verbal!!
In 1918, The Air ministry, in it's wisdom, came up with this solution. Signalers would be issued with a cloth badge, to be worn on their tunic, giving the wearer the authority to speak, address or pass on, a communication of any sort, directly. The same badge, while the wearer was on duty, would also excuse them from repeatedly saluting the officer(s), if there were more than one `over' in the messaging sequence.
There exists Ministry of Supply and Air Ministry documents showing that this badge was manufactured and issued, But nothing stated officially about the reason for issue, it seems they were just `Generally Accepted' rules of conduct, that are, with this badge, still in use, in today's Royal Air Force.