Well, looking at how he moves, or behaves, that's what I've read somewhere, maybe it was here, or maybe I saw it in some BRINK video.
If a Heavy does some Light moves, then we might have a problem.
If a Light does'nt do his Light stuff, and wont move at Light speed (lol), then we might have a problem.
If a guy is constantly behind someone, like, really close (backstab if it's in), then we might have a problem.
If a guy is not going to the front lines with everyone else, while acting suspiciously, then we might have a problem.
Houston, I think we have a problem, over.