It shall be the duty of every person to whom a taxicab license is issued to post the license certificate in a prominent place upon the premises of the headquarters from where the business is carried on, and to keep the license certificate so posted so long as the business is carried on thereunder. The licensee shall not permit the license to be obscured or concealed in any way, so that the license will not be readily visible at all times to persons lawfully present on the premises.
('68 Code, § 52.28) Penalty, see § 111.99