No person shall operate, conduct, control, manage or otherwise carry on any shoe shine parlor or stand in the City of Los Angeles unless there is posted and maintained therein or thereon in a conspicuous place, clearly visible by the public, a sign listing the price of each and every service rendered by such business, and no such person shall charge or attempt to charge any amount different from that appearing on such sign for any service rendered. The lettering on such sign shall be of uniform size with the letters not less than one inch in height.