This is why i engraved my Form 1 SBRs:
§ 479.102 How must firearms be
identified?
(a) You, as a manufacturer, importer,
or maker of a firearm, must legibly identify
the firearm as follows:
(1) By engraving, casting, stamping
(impressing), or otherwise conspicuously
placing or causing to be
engraved, cast, stamped (impressed)
or placed on the frame or receiver
thereof an individual serial number.
The serial number must be placed
in a manner not susceptible of being
readily obliterated, altered, or removed,
and must not duplicate any
serial number placed by you on any
other firearm. For firearms manufactured,
imported, or made on and after
January 30, 2002, the engraving,
casting, or stamping (impressing) of
the serial number must be to a minimum
depth of .003 inch and in a print
size no smaller than 1⁄16 inch; and
(2) By engraving, casting, stamping
(impressing), or otherwise conspicuously
placing or causing to be engraved,
cast, stamped (impressed), or
placed on the frame, receiver, or barrel
thereof certain additional information.
This information must be placed in a
manner not susceptible of being readily
obliterated, altered or removed. For
firearms manufactured, imported, or
made on and after January 30, 2002,
the engraving, casting, or stamping
(impressing) of this information must
be to a minimum depth of .003 inch.
The additional information includes:
(i) The model, if such designation
has been made;
(ii) The caliber or gauge;
(iii) Your name (or recognized
abbreviation) and also, when applicable,
the name of the foreign
manufacturer or maker;
(iv) In the case of a domestically
made firearm, the city and State
(or recognized abbreviation thereof)
where you as the manufacturer
maintain your place of business, or
where you, as the maker, made the
firearm.
ATF Publication 5300.4