This past January I was with a great provider in her NY hotel room and she left the drapes open. There were windows just across the alley from which anyone there could have seen us "in flagrante dilecto," but I never saw anybody.
A lot of this was going on at a new hotel in Manhattan's meat packing district called The Standard. It was built with floor-to-ceiling glass for the outer walls of each room. It also was built right over the High Line, an old elevated rail system that's been turned into a pedestrian walkway and park. So people at the Standard started fucking up against the glass windows so strollers could see them. It became such a well-known spectator event that The Standard put a card in each room warning guests about losing their privacy. When my SO and stayed there a couple of years ago we had sex, but not up against the window.