California Code, Vehicle Code - VEH § 5032

(a) The application for a special license plate for a motorized bicycle shall be made before the motorized bicycle is operated or moved upon a highway, except that, upon the retail sale of a motorized bicycle when there is no license plate, the operator may operate the motorized bicycle for a period of five days from and including the date of sale, at which time application shall be made to the department for a special license plate. If the fifth day should fall on Saturday, Sunday, or a holiday, the application shall be made on the first business day thereafter.

(b) The five-day operating provision set forth in subdivision (a) shall apply only if the operator has in his immediate possession evidence that the motorized bicycle was purchased within the last five days including the date of sale.