All information was taken from the ATF Publication 5300.4 - section 479.102 " How must firearms be identified?"
Any gun manufactured, imported, or made on and after January 30, 2002 must have manufacturer information placed at a minimun depth of .003” with a height no smaller than 1/16”.
This information must be engraved, cast, stamped (impressed), or otherwise conspicuously placed on the frame, receiver, or barrel.
Required information on an SBR is the model (if such designation has been made), 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.