[conservator]

Jerry, you are quite right.
Three types of brooch were used, all based on the letter 'N', surmounted by different devices, representing the different services: St Edwards crown - Army; Naval crown - RN & RM and RAF eagle - RAF. These badges, I suspect, cost very little to make; they look to have been made from a cast base metal and possibly plated with a locking pin attached. From the front, and at a distance, they look like silver badges with marcasite type stones set into the 'N'; close up, their probable low cost becomes apparent. From the rear, they look rather crude too. It is likely that the initial issue of these badges reflected the establishment to which a member of staff was posted; and, they would continue to wear the badge, even if on loan to the establishment of another service , but could exchange their badge if a move became permanent. I have a feint memory of NAAFI staff, on loan to RAF Brawdy from Castlemartin Ranges in Wales, wearing a badge with the crown rather than the eagle. I also have a vague recollection of being told by a NAAFI girl that her badge was the only one she had and it would have to be returned to NAAFI when she left. As the quality of the badges was fairly poor, one would expect that staff would be allowed to keep them upon leaving NAAFI.
I don't know whether better quality badges were issued to more senior members of staff or whether, upon leaving NAAFI, senior staff were presented with badges in a similar way to plaques etc. being presented.
It may be that better quality badges do exist, though I haven't seen any?
George