California Code, Vehicle Code - VEH § 27906.7

(a) A school district, county office of education, or charter school using a zero-emission schoolbus to transport pupils at or below the 12th-grade level may place signage on the rear of the zero-emission schoolbus that identifies the schoolbus as a clean air zero-emission bus.  The signage may specify the fuel type of the zero-emission schoolbus.

(b) The Department of the California Highway Patrol may issue guidelines governing the size and placement of the signage described in subdivision (a).