Yes the NYC subway is 600 volts DC. The car lighting is accomadated by wiring 5 120 volt fixtures in series. Same premis with some of the track and tunnel lighting. Most temporary lighting is simply tapped off the third rail and wired the same way.
As far as DC in use in other types of bldgs, I have seen dc in use for large motors in older manhattan high rises. But they are rapidly being replaced. The only place it commonly found is for elevator motors but there is an ac motor generator usually attached or close by.
