[Brush Buster]

Recently acquired Parker Brothers 16 Ga. Hammer gun ,Serial 14290 , I have been sorting out the markings etc. and have a question about a rather large Capital " M " located on the Barrel flat ,with the barrels off and laying across my lap ,the " M " is located on the bottom left hand corner and on the other Barrel flat is a small O stamped which I assume stands for Twist Steel barrels as the gun in " The Parker Story ,Page 100 Fig. 3/23 ,although the O is stamped right beside the Large letter T on that particular gun ! Has anyone seen this large Capital M before and if so ,do you have any idea of it's meaning ? Thank You ; Russ