Each person who holds a hearing-aid dealer's or fitter's license and engages in the practice of dealing in the fitting of hearing aids shall display such license in a conspicuous place in his office or place of business at all times. Each person who maintains more than one office or place of business shall post a duplicate copy of the license at each location. The board shall issue duplicate copies of a license upon receipt of a properly completed application and payment of $1 for each copy requested.