If the PMF is already marked by a non-licensee with a unique identification number that otherwise meets the marking standards in 478.92 (e.g., depth and size requirements), FFLs may adopt the unique PMF serial number by marking their abbreviated license number (first three and last five digits of their FFL number) as a prefix to the number, immediately followed by a hyphen (i.e., “12345678-[unique identification number]”), provided the unique identification number is not duplicated on any other firearm of the licensee.

If the unique identification number marked on the PMF does not comply with 478.92, the licensee may not adopt the unique identification numbers and must mark the firearm as required by 478.92(a)(2).