7.4.2 Additional information. Certain additional information must also be conspicuously placed on the frame, receiver, or barrel of the firearm by engraving, casting, stamping (impressing), that is, they must be placed in such a manner that they are wholly unobstructed from plain view. For firearms manufactured on or after January 30, 2002, this information must be to a minimum depth of .003 inch. The additional information includes:
(1) The model, if such designation has been made;
(2) The caliber or gauge;
(3)
The manufacturer’s name (or recognized abbreviation); and
(4)
The city and State (or recognized abbreviation) where the manufacturer maintains its place of business.122
ATF National Firearms Act Handbook