No person shall operate or maintain upon or adjacent to any public sidewalk any hat block or other device which revolves or rotates by means of power, unless such hat block or other device is separated from the sidewalk by a suitable barrier to prevent persons using the sidewalk from coming in contact with such hat block or other revolving device, or unless such hat block or other revolving device is screened with a metal screen or a mesh not greater than one quarter of an inch in size.