Some Other Ranks have Trade Badges.
Most Officers don’t, apart from Aircrew and the Medical/Religious.
Thus, in the Officers Mess, there’s no visual way of discerning who is Admin, Eng, ATC, FC, Supply, PEdO, Catering and a few others I may have missed. I always liked the old RN system of coloured bands between the gold rings ... Wasn’t it Green for Electrical Engineers, etc, and nothing for the Executive Branch (aka Ship-Drivers!).