If we are fighting a more conventional type of war, once captured by the enemy they can expect you to state your name, rank, service number,...etc (big 6).
In which case, no matter what you are wearing, when you state your rank as Flt Sgt, Fg Off, Flt Lt, Sqn Ldr, etc it is fairly obvious that you are in the RAF.
Only Sgts have some chance of passing unnoticed....and I wouldn't hold your breath, no doubt the service number would be a giveaway.
I could never understand why the Iraqi interrogations seemed so keen to determine which of Peters and Nichol were the pilot or Nav - other than that it was a crack in their "sticking to the big4/6" approach. Given that the service numbers had been offered up, a simple check in a copy of the RAF list, obtainable at the time from HMSO, would have told them who was the pilot....