No.5 Mk.I - (F) mark?

I have a 1947 No. 5 Mk. 1, bought it 20+years ago. All serial numbers are matching, good wood and metal finish, nice bore. I have always wondered - what does the (F) stand for that is stamped on the rifle? I checked a few Lee Enfiled sites about the various stamps and marks but did not come up with anything. Thanks in advance!

The (F) stands for the Royal Ordnance Factory - Fazakerley in England - i.e. the place of manufacture.

Would you share the serial number or at least the month of manufacture of the No5?