Washington Revised Code Title 9. Crimes and Punishments § 9.41.328. Imprinting a firearm or unfinished frame or receiver

(1) A federal firearms dealer or other federal licensee authorized to provide marking services for firearms may imprint a firearm or unfinished frame or receiver with a serial number.

(2) The firearm or unfinished frame or receiver shall be imprinted with the licensee's abbreviated federal firearms license number as a prefix (which is the first three and last five digits) followed by a hyphen, and then followed by a number as a suffix, e.g., “12345678-(number).” The serial number must be placed in a manner that accords with the requirements under federal law for affixing serial numbers to firearms, including the requirements that the serial number be at the minimum size and depth, and not susceptible to being readily obliterated, altered, or removed.

(3) The serial number must not duplicate any serial numbers placed by the federal firearms dealer or other federal licensee on any other firearm or unfinished frame or receiver.

(4) Whenever a federal firearms dealer or other federal licensee imprints a firearm or unfinished frame or receiver with a serial number, the licensee shall retain records that accord with the requirements under federal law in the case of the sale of a firearm.