In the June 1981 issue of GUNS REVIEW an article written by Udo E. Troster titled" BRITIAN'S SECRET PROOF MARKS" where there is a full page written about the Birmingham "private view marks" in the 4th paragraph quote:

"The Birmingham Proof Master Colonel Playfair died in 1941 and the marking system seems to have fallen into disuse until the present Proof Master, R.P. Lees, was appointed. He modified the old mark and reintroduced it with effect from 1 January 1950.......The letter code used for 1950 was A".