1938 S/42 "A" stamp?

[waltherguy]

First and foremost... Hello all! Sad to say, I have not logged onto the forum since 2009 Life, Career changes, selling off the collection, etc... Glad to be back! SO all that said, Starting to slowly rebuild the collection and ran across a 1938 Mauser that really has me scratching my head.. First glance I noticed a un numbered side plate and takedown pin and thought.. meh, it's a shooter... But then I noticed a very odd large letter "A" stamped next to the serial number on the left side, and also on the lower part of the gun???? I'm really baffled... Any ideas?

Thanks much!