All solicitors shall, at all times when so engaged, carry their license on their persons. All other licensees shall post their licenses in their place of business near the licensed activity; provided, however, that, in the case of machine or other device licensing, the city may provide a sticker for the current license year which shall be affixed to each machine or device requiring the sticker in a location that is visible at all times by patrons. All licensees shall display their licenses upon demand by any officer or citizen.