(1) A school bus may be operated by the district or other public agency for the conveyance of pupils or may be privately operated by a carrier to provide such conveyance of pupils under contract with a district or other public agency.
(2) Every school bus shall bear on the front and rear of the bus a plainly visible sign containing the words "school bus" in letters at least 8 inches in height.
(3) When a school bus is operated on a highway for purposes other than transporting pupils to and from school or for school functions, all markings identifying it as a school bus shall be concealed.