It is unlawful and an offense against the city, for any person to obstruct the free, convenient and normal use of any public sidewalk, street, highway, bridge, alley, road or other passageway, or the entrance, corridor or passage of any public building or structure by impeding, hindering, stifling, retarding or restraining traffic or passage thereon or therein after having been requested by a police officer to move on. (Prior code § 19-7)