27 CFR 478.92(a)(1)(i), as amended, states that manufacturers and importers must legibly identify each firearm they manufacture or import by placing on the frame or receiver the serial number and either name, city and State or name and abbreviated federal firearms licensee (FFL) number (i.e. first three and last five digits) as a prefix, followed by a hyphen and the unique identification number assigned to the firearm.  

478.92(a)(2), as amended, states that privately made firearms (PMFs) not previously identified by another licensee must be identified by the licensee receiving or acquiring the PMF by placing, or causing to be placed under the licensee’s direct supervision, an individual serial number on the frame or receiver that must begin with the licensee’s abbreviated Federal firearms license number, which is the first three and last five digits, as a prefix to a unique identification number, followed by a hyphen, and the unique identification number. 

478.92(a)(4)(iii)(B), as amended, allows licensed  manufacturers and importers to adopt the serial number or other identifying markings previously placed on an imported or remanufactured firearm sold, shipped, or otherwise disposed of to a non-licensee that otherwise meets the requirements of 478.92; however, the licensee must place, or cause to be placed, on the frame or receiver either their name (or recognized abbreviation), and city and State (or recognized abbreviation) where they maintain their place of business; or their name (or recognized abbreviation) and abbreviated Federal firearms license number, which is the first three and last five digits, individually (i.e., not as a prefix to the serial number adopted) after the letters ‘‘FFL’’, in the following format: ‘‘FFL12345678’’. 

478.92(a)(4)(i), as amended, provides an exception for the above marking requirements described as “Alternate means of identification” and states:

“The Director may authorize other means of identification to identify firearms upon receipt of a letter application or prescribed form from the licensee showing that such other identification is reasonable and will not hinder the effective administration of this part.”