Help me to look like a smartarse – Cyma content.

I just had this from a fellow Riley owner (yes, I have asked for a photo). Any ideas chaps?

HI Alec, I know you are keen on watches.
It is a small Omega ladies’ wristwatch with florescent hands and spots by the numerals.
On the back is a small number presumably from Omega 8983-2817, but the interesting bit, it is marked with the broad arrow
A.T.P.
49692
Can you tell us anything about it, may be from Tricia’s mum who was in WAAF. Cheers David