Any person, in the United States, in a situation where he is surrounded by a massive police presence on a transportation platform, and is paranoid about the police shooting him, is really in a really bad place mentally. A sane person is very very concerned, they would figure there is a reason all the police were there and that there was some threat they shoud be really alarmed about. Yeah, in that situation, you look around, pick one of the cops out, and ask "Hey, is something going on?".If the answer is yes, then you ask "Should I leave, and in what direction?". And if they send you in some direction, go that way promptly. Unless you see a really good reason not to. Your train arriving at the platform in two minutes is NOT a really good reason - you'd rather miss the train than stay there and find out the cops are waiting for someone who's on it.But don't waste time asking WHAT is going on - aside from the fact that they should not tell you (operational security), there is also the fact that they shouldn't tell you (keeping focused on what they are doing). Getting an innocent civilian out of the way is part of their job; help them with that part by determining where "out of the way" is and going there.