Every building which shall appear to the director of public works to be especially dangerous in case of fire by reason of bad conditions of walls, overloaded floors, defective construction, decay or other causes, shall be held to be an unsafe building, and the director of public works, in addition to proceeding as provided in § 9-51, shall also affix a notice of the dangerous character of the building in a conspicuous place on the exterior wall thereof, and any person removing, defacing or disturbing such notice so affixed shall be guilty of a misdemeanor.