The final rule amends 27 CFR 478.92(a)(2) and explains that an acceptable method of identifying a polymer frame privately made firearm (PMF) is by placing a serial number on a metal plate that is permanently embedded into a polymer frame or receiver, or other method approved by the Director.
A marking variance can be applied for under 478.92(a)(4), as amended, which states:
Exceptions—(i) Alternate means of identification. 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.