I know to the untrained eye, all Orthodox Jewish men look the same; black suits, hats, and beards. But if you look at the details, it's pretty easy to tell the difference between certain sects. I'll tell you how to tell a Satmar from a Lubavitcher from a regular Orthodox when they're outside their own neighborhoods.
It's all in the face and the attitude. If he's nervous, a bit uptight, and clearly doesn't want to interact with you, he's a Satmar. If he's got a serious, businesslike expression and manner (and probably on his cellphone), he's Orthodox. If he's happy, maybe smiling, and has a cool, casual confidence about him, he's a Lubavitcher.
There's also the distinctive hats each group wears, but I'll get into that another time. Now you can tell the difference, and won't confuse me for a 'regular' Orthodox guy. You can tell by my smile. :)