Cal. Veh. Code § 9872

No person shall intentionally deface, destroy, or alter the hull identification number of a vessel required to be numbered under this chapter without written authorization from the department; nor shall any person place or stamp any serial or other number or mark upon an undocumented vessel which might interfere with identification of the hull identification number. This does not prohibit the restoration by an owner of an original number or mark 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 vessels or new parts thereof.