The BATFE has promulgated regulations regarding the manufacture of a class 3 firearm. Specifically, the requirements for identification/engraving are set forth in BATFE Publication 5300.4 -27 CFR 479.102
The regulation specifies that any gun manufactured, imported, or made on and after January, 2002 must have the manufacturers information engraved, cast, stamped by impression, at a minimum depth of .003″ with a height no smaller than 1/16″ on the frame, receiver, or barrel.
The required information on an Short Barreled Rifle (SBR) or Short Barreled Shotgun (SBS) is:
1. The model (if such one exists),
2. Caliber or gauge,
3. The manufacturer’s name (or recognized abbreviation), and if applicable
4. The city and state (or recognized abbreviation), where you as the manufacturer made the firearm, if it is domestically manufactured.
UPDATE: Effective 1/20/09, the BATFE has reversed its decision to allow abbreviations of trust names. The entire trust name must now be engraved. Ironically, an individual on Ar-15.com recently posted an error letter, dated 1/20/09, for his application because he abbreviated his trust’s name. See the error letter here. However, one may be able to obtain a variance from the BATFE for the required marking. If information on marking variances, see Guide to Marking Variances.