Publication
ATF 5300.4 in 27 CFR 479.102 (page 92) describes what is necessary to engrave on a SBR or SBS when one is manufacturing. This is not necessary if you purchase one that is already manufactured as it will have been done for you.
1) On the Frame or Receiver the Serial number;
2) on the frame, receiver, or barrel the following additional information;
A)The model;
B)The caliber or gage;
C)Your name or name of the Trust in the case of a Trust (no abbreviations are permitted for the Trust name);
D)The city and state (you can abbreviate the state with the official 2 digit state code)
The above mentioned information must be engraved, casted, stamped (impressing) or otherwise conspicuously placed or caused to be engraved, cast, stamped (impressed) or placed to a minimum depth of .003 inch and in a print size of the Serial number shall be no smaller than 1/16 inch.