Of course it means more than just "I cut you off," but I had to make this a little bit harder.  This is the universal thumbs up symbol. However Brazilians use this one a lot.  It can also mean:

I think many people have hear the story that this gesture originated from Romans and the Coliseum.  The Romans would use a thumbs up gesture to mean "spare him" and thumbs down to mean "kill him".  From what I understand, this is only half right.  The thumbs down gesture is correct, it mimics the action of stabbing the victim.  The thumbs up wasn't used, however.  The thumb was actually hidden, held with the other fingers.