Every school bus owned or operated by or for a school or school district shall bear upon the front and rear thereof plainly visible signs containing the words “school bus” in letters not less than eight inches in height. When any such vehicle is being operated upon a highway for purposes other than the actual transportation of children either to or from school or in connection with school activities, all markings thereon indicating “school bus” shall be covered or concealed.
(SDCL § 32-32-2) (Prior Code, § 17-387)