How did the act of sticking your thumb up at traffic become the official signal for asking for a free ride?
KnK
No offense, but I am sure trying to get a lift using your middle finger wouldn’t have a high success rate. 
It shows the direction in which you want to go while still facing the traffic.
quality!
Depends where you are. You’d have as much success with this method in Israel than if you thumbed as it is tantamount to giving the finger anyway.