In addition to the requirements of section 81-1021, all motor vehicles used by the Nebraska State Patrol for patrol purposes shall be (1) equipped with a flashing red light on the top thereof with controls therefor readily accessible to the driver and (2) on the back thereof indelibly and conspicuously lettered with the words State Patrol in plain letters of reflective material not less than two inches in height and with not less than one-fourth inch stroke.