I used to see NYPD putting together one of these "show of force" things at Columbus Circle every once and a while. They sat there for like an hour getting all the patrol cars together and then headed out. Here's a couple of youtube clips if you're wondering what it looks like:

http://www.youtube.com/watch?v=DFMgi...eature=related

http://www.youtube.com/watch?v=eB29H...eature=related