(a)   Each watchman, trainman or other agent of any railroad or railway company, if and when stationed at a railway crossing within the corporate limits of the City, shall be vested with authority to regulate and control traffic of vehicles at such crossing where he is so stationed. It shall be his duty to direct the movement of traffic at such railway crossing in such a manner as will facilitate the movement of traffic and prevent congestion and accidents, and to stop all movement of vehicles at the crossing when any engine, car or conveyance of the railway company approaches the crossing upon the tracks, by arm signals or by holding a stop signal in his hand extended straight out from his shoulder while facing the street.
   (b)   No person shall violate any order or signal of any such watchman.
(1958 Code § 16.6)