California Code, Vehicle Code - VEH § 9853.3

The certificate of number for vessels less than 26 feet in length and leased or rented to another for the latter's noncommercial use of less than 24 hours may be retained on shore by the vessel's owner or his representative at the place from which the vessel departs or returns to the possession of the owner or his representative.  A copy of the lease or rental agreement signed by the owner or his authorized representative and by the person leasing or renting the vessel shall be carried aboard the vessel at all times during use.