Whenever a signal has been given to let down the gates or other contrivances located at the crossing of any street by a steam railway track in the City, or whenever gates or contrivances are in fact down for the approach of any engine, train or handcar which is crossing or about to cross any such street, no person shall go or stand within the enclosure made by such gates or contrivances so let down or about to be let down, and nor shall any person ride, push, draw, back, lift, place or drive any horse, cart, wagon, velocipede, bicycle or other vehicle within the enclosure made as aforesaid, or upon or against the gates or contrivances after such signal has been given or the gates or contrivances are in the act of being let down, or are in fact down.