Diana,
Depends on what you're shooting. If your shooting a private building, then yes, they may come out and ask you to stop shooting it. If you're in the middle of Times Square, then no, they can't ask you to stop. With that said, when I'm in a "place" where I think I might be asked to stop shooting or using a tripod, I ALWAYS have the camera already set on the tripod head, ready to go and then place it and start shooting, by the time you get your three exposures and anybody comes out, you're done. So set your camera for 3 exposures, f16, ISO 100 and Aperture priority and shoot away.
Really depends on where and what you're shooting, but if you're fast, then you should have no problems.
Here's an "official" paper from the NY Police Dept. to their officers about filming and tripods: http://i.imgur.com/qXQWcQw.jpg
Good Luck,
Rich