Cal. VEH § 5010

Notwithstanding any other provision of this code, when a motor vehicle which is leased to a school district for use as a schoolbus, as defined in Section 545, temporarily reverts to the possession and control of the lessor, and if the motor vehicle thereafter becomes subject to registration, the lessor may, as an alternative to such registration, secure a temporary permit to operate the vehicle in this state for any one or more calendar months. Such permit shall be posted upon the windshield or other prominent place upon the vehicle, and shall identify the vehicle for which it is affixed. When so affixed, such permit shall serve in lieu of registration. If such a lessor operates the motor vehicle under a temporary permit issued pursuant to this section, he shall notwithstanding the provisions of Section 5000 continue to display on the vehicle the exempt license plates issued to the vehicle as a schoolbus. Upon payment of the fees specified in Section 9266, the department may issue a temporary permit under this section.