You've lost the others on a table saw.

Origins are quite old indeed. During the middle ages, in conflict the English army (opposing the French, I believe) were far superior with the long bow. Bows at the time were made from the wood of the Yew tree. Upon seeing the devistation, officers of the French forces ordered any archers caught to have their index and middle fingers removed, hence making plucking the strings of the bows impossible.
The British, in defiance (or possibly to add insult to injury) would proudly display their intact digits during battle proving to their foes that they could still, indeed,
"Pluck the Yew"

In the UK it's taken to mean "up yours" (I'll leave it to you to guess what "yours" might be) as in take your opinions and shove them where the sun don't shine...

and yes, it is quite offensive!

I also found this:
http://www.dogsonacid.com/showthread.php

In Japanese sign language (JSL) it is the sign for older brother.

In Texas, it means go "F@#K YOURSELF". "F@#K YOU" and so on. It is a very insulting gesture performed to instigate an illicet reaction, however close friends may get away with it as a freindly gesture if your just joking around. If someone gives you the finger however, more than likely you did somthing stupid enough to illicit that response from someone else.

I LOVE YOU

It is certainly thousands of years old, being referred to in Ancient Roman literature as the digitus infamis or digitus impudicus. Performing this gesture is also called "flipping the bird" in countries where "the finger" is used. In other regions, "flipping the bird" refers to the raising of the middle and index finger with the back of the hand directed at the recipient. It can also mean "Victor" (see V Sign, below) in some countries, which is not to be mistaken for the "Peace" gesture, which is done with the palm facing the recipient of the gesture, but in Britain and some other countries it is an offensive gesture, equivalent to "the finger".

When this gesture is made with the palm facing forward, it is known to Chaotes practicing Lovecraftian magick as the "Sign of Kish".

http://www.search.com/reference/Type_of_gesture

The "one-finger salute," or at any rate sexual gestures involving the middle finger, are thousands of years old. In Gestures: Their Origins and Distribution, Desmond Morris and colleagues note that the digitus infamis or digitus impudicus (infamous or indecent finger) is mentioned several times in the literature of ancient Rome. Turning to our vast classical library, we quickly turn up three references. Two are from the epigrammatist Martial: "Laugh loudly, Sextillus, when someone calls you a queen and put your middle finger out."

In the other reference Martial writes that a certain party "points a finger, an indecent one, at" some other people. The historian Suetonius, writing about Augustus Caesar, says the emperor "expelled [the entertainer] Pylades . . . because when a spectator started to hiss, he called the attention of the whole audience to him with an obscene movement of his middle finger." Morris also claims that the mad emperor Caligula, as an insult, would extend his middle finger for supplicants to kiss.

http://www.straightdope.com/classics/a980904.html

It means have yourself a great day!

Actually, in the US, raising your middle finger is a profane action that means someone is visibly upset with you.

Bottom line: It's bad manners & inappropriate behavior.

It depends what country you're in... in North America it's considered a curse, "throwing the finger" -- which you might do from the safety of your car, when somebody cuts you off, or impatiently honks at you. Trouble makers might taunt the police with this gesture.

It is a rude gesture from someone with a limited vocabulary!