California Vehicle Code
(a) Every operator of transportation service which is exempt from regulation as a charter-party carrier of passengers pursuant to subdivision (k) or (l) of Section 5353 of the Public Utilities Code, and which furnishes that transportation service in a bus, shall obtain a carrier identification number from the Department of the California Highway Patrol. Application for a carrier identification number shall be on a form furnished by the Department of the California Highway Patrol.
(b) (1)The carrier identification number so obtained by the
operator shall be displayed on both sides of each bus used in that transportation service.
(2) The display of the carrier identification number shall be in sharp contrast to the background, and shall be of a size, shape, and color as to be readily legible during daylight hours from a distance of at least 50 feet.
(3) The carrier identification number shall be removed before the sale, transfer, or other disposal of the bus.