Flash - the 'ac' designation means it was made by Walther. byf means Mauser, and I believe 'cg' means the Spreewerke plant. The weird configuration of horizontal lines might well be the german eagle, which is the proof mark. The Germans would usually stamp or number each part of each rifle/pistol, so the numbers 359 should appear on most of the parts.
I think I'm right, but could be wrong. Mikey.