California Code, Vehicle Code - VEH § 5017

(a) Each identification plate issued under Section 5016 shall bear a distinctive number to identify the equipment, logging vehicle, trailer, semitrailer, or implement of husbandry for which it is issued.  The owner, upon being issued a plate, shall attach it to the equipment, logging vehicle, trailer, semitrailer, or implement of husbandry for which it is issued and shall carry the identification certificate issued by the department as provided by Section 4454.  It shall be unlawful for any person to attach or use the plate upon any other equipment, logging vehicle, trailer, semitrailer, or implement of husbandry.  If the equipment, logging vehicle, trailer, semitrailer, or implement of husbandry is destroyed or the ownership thereof transferred to another person, the person to whom the plate was issued shall, within 10 days, notify the department, on a form approved by the department, that the equipment, logging vehicle, trailer, semitrailer, or implement of husbandry has been destroyed or the ownership thereof transferred to another person.

(b) Upon the implementation of the permanent trailer identification plate program, all trailers except those exempted in paragraphs (1) and (3) of subdivision (a) of Section 5014.1 may be assigned a single permanent plate for identification purposes.  Upon issuance of the plate, it shall be attached to the vehicle pursuant to Sections 5200 and 5201.

(c) An identification certificate shall be issued for each trailer or semitrailer assigned an identification plate.  The identification certificate shall contain upon its face, the date issued, the name and residence or business address of the registered owner or lessee and of the legal owner, if any, the vehicle identification number assigned to the trailer or semitrailer, and a description of the trailer or semitrailer as complete as that required in the application for registration of the trailer or semitrailer.  For those trailers registered under Article 4 (commencing with Section 8050) of Chapter 4 on the effective date of the act adding this sentence that are being converted to the permanent trailer identification program, the identification card may contain only the name of the registrant, and the legal owner's name is not required to be shown.  Upon transfer of those trailers, the identification card shall contain the name of the owner and legal owner, if any.  When an identification certificate has been issued to a trailer or semitrailer, the owner or operator shall make that certificate available for inspection by a peace officer upon request.

(d) The application for transfer of ownership of a vehicle with a trailer plate or permanent trailer identification plate shall be made within 10 days of sale of the vehicle.  The permanent trailer identification certificate is not a certificate of ownership as described in Section 38076.