No person shall operate or park on any highway any vehicle for the primary purpose of displaying advertising; however, in the case of public undertakings, or undertakings sponsored by charitable, benevolent, or religious organizations, the safety-service director shall be authorized to issue temporary permits for the advertising display on vehicles where no charge is made for the use of the vehicle. In granting any such permits, the safety-service director may impose such limitations and restrictions as may be conducive to the public welfare.
('73 Code, §§ 73.11 and 74.01) Penalty, see § 70.99