California Code, Penal Code - PEN § 23915

(a) Any person may place or stamp on any pistol, revolver, or other firearm any number or identifying indicium, provided the number or identifying indicium does not change, alter, remove, or obliterate the manufacturer's name, number, model, or other mark of identification.

(b) This section does not prohibit restoration by the owner of the name of the maker or model, or of the original manufacturer's number or other mark of identification, when that restoration is authorized by the department.

(c) This section does not prevent any manufacturer from placing in the ordinary course of business the name of the maker, model, manufacturer's number, or other mark of identification upon a new firearm.