California Code, Vehicle Code - VEH § 10750

(a) No person shall intentionally deface, destroy, or alter the motor number, other distinguishing number, or identification mark of a vehicle required or employed for registration purposes without written authorization from the department, nor shall any person place or stamp any serial, motor, or other number or mark upon a vehicle, except one assigned thereto by the department.

(b) This section does not prohibit the restoration by an owner of the original vehicle identification number when the restoration is authorized by the department, nor prevent any manufacturer from placing in the ordinary course of business numbers or marks upon new motor vehicles or new parts thereof.