On and after the passage of this act it shall be unlawful for any person to let, rent, lease, or conduct any tenement-house or rooming-house, in any city of the first class, unless a license therefor has been issued by the Bureau or Board of Health, in accordance with the provisions of section forty-four of this act, and unless such license is at all times displayed in a conspicuous place upon the walls within and close to the outer entrance of the house.
53 P.S. § 15045