Disobey traffic control device - Violation 1110-A in NYC

I was on 42nd Street and 5th Avenue in Manhattan NY and I made a left turn which was illegal. The sign says "NO TURNS except Buses" from 5th Avenue making a left to 42nd Street. There was a large bus in front of me that made a left turn as well but I could not see the sign that prohibits this turn. In addition, the officer was a highway patrol cop that pulled me over was not in his vehicle,when he pulled me over he was on foot. He pulled me over on 42nd Street which is about 150 feet from the corner where the NO TURN sign is posted so how can the officer even see that I made the turn. So my question is: 1) Wouldn't it be a burden of proof for the officer to state that he saw me make the turn, 2) The bus obstructed the sign, 3) Can an officer pull me over on foot. You help is appreciated.