California Code, Vehicle Code - VEH § 5015

(a) The application for an identification plate for special construction equipment, special mobile equipment, cemetery equipment, and any logging vehicle shall be made before that piece of equipment is moved over a highway.

(b) The application for an identification plate for a cotton trailer or a farm trailer as specified in Section 36109, a vehicle that is farmer-owned and used as provided in subdivision (b) of Section 36101, a motor vehicle that is farmer-owned and operated and used as provided in subdivision (a) of Section 36101, or an automatic bale wagon operated as specified in subdivision (a) or (b) of Section 36102 shall be made before any such piece of equipment is moved over a highway.

(c) The application for a permanent trailer identification plate, as described in Section 5014.1, shall be made prior to the equipment or vehicle described in subdivision (a) being moved, towed, or left standing on any highway or in any offstreet public parking facility.