All signs, banners, flags, or advertisements mentioned in Sections 13.24.020 and 13.24.030, extending over or upon any public sidewalk, shall be erected and maintained at a distance of not less than ten feet above such sidewalk, and all electrical display signs and other signs shall be of substantial construction and shall be attached to or suspended from iron supports securely fastened to a substantial building or structure in such a manner as to prevent the collapse or falling thereof or to in any way endanger the public. (Ord. 840, 1939)