The provisions of sections 71-3201 to 71-3213 shall not prevent the proper local authorities of any city or village, by ordinance or other proper manner within the exercise of the police power of such city or village, from appointing special policemen for such purposes and subject to such proper and reasonable restrictions, terms, and conditions as such local authorities may prescribe; but such police power shall not be so exercised as to infringe upon or nullify any license duly issued and held under the provisions of sections 71-3201 to 71-3213.