Permits under § 105-2 may be limited to hours, routes, purposes or character of use, may extend to general classes of officers or employees, and may be canceled or revoked at any time without notice. The burden of proof shall be upon any officer or employee given a written permit under subdivisions (4) or (5) of § 105-2 to prove, in any proceedings, that the officer or employee had, at the time of so using, operating, or driving any such motor vehicle, an unrevoked written permit to so use, operate, or drive the same. Likewise, the burden of proof shall be upon any person conveyed in any such motor vehicle as provided in subdivision (6), § 105-2 to prove, in any proceedings, that the officer, or head of the department, commission, board, bureau, agency, or instrumentality, controlling or possessing such motor vehicle certified to such use and filed such certificate as required by subdivision (6).