Section 23. Every stairway of every building shall be kept free and unobstructed, and any person who permits any article to remain in any stairway of any building in such a manner as may impede the egress of any person lawfully in said building or the ingress of any person lawfully entitled to enter said building shall be punished by a fine of not more than five hundred dollars. The existence of any article in any such stairway in any building shall be prima facie evidence that it was placed or permitted to remain therein by the owner, lessee, tenant or occupant of the building.