When manufacturing a class 3 firearm that is restricted by the NFA it is important to follow the guidelines found in the ATF Publication 5300.4 – section 479.102 ” How must firearms be identified?”
Generally, 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 SBR is the model (if such one exists), caliber or gauge, and the manufacturer’s name (or recognized abbreviation). Also for a domestically made (SBR) the city and state (or recognized abbreviation), where you as the manufacturer made the firearm.