Fun game: if you see a good crowd shot, watch how individual sections of the crowd move. You should eventually spot at least one guy that's not moving. He may be wearing a jacket, probably has his hands in his pockets, and usually isn't looking in the same direction as the crowd. Move two spaces over and two spaces up, generally speaking. In one direction or another, you'll probably find another similar dude. Keep searching until you see them positioned like pawns on a chessboard positioned throughout the crowd, curiously not following the natural movements of such a gathering and watching the crowd instead of the crowd's current focus. These are secret police.
