Bit of thread drift, but what about using post nominals to indicate an order or decoration (OBE, DFC etc)? Never had anything like that myself but I'm damn sure I would use them at every opportunity if I had!
In 1943 my dad was a WO2 in the Military Police in North Africa. He was given the job of arranging security for King George VI when he was visiting the area where dad was serving. At the end of the visit dad was marched in for a brief audience with HM, who thanked him and presented him with the ribbon of the Royal Victorian Medal for personal services to the monarch (he got the actual medal at the Palace in 1946). One week later his commission came through. Had he already been an officer when he got the medal he would in fact have received the MVO instead. On return to his civilian job as an AA inspector, his employers thought it would be rather good to emphasise the fact that one of their staff had letters after his name, but discovered that there was no entitlement to post nominal letters for the RVM, so thereafter all his official correspondence came addressed to Inspector *** , MVO, which of course he was not entitled do. Dad used the post nominals shamelessly for the rest of his life, and to be honest I don't think it was that much of a crime!