This (from this site) is a gesture made by President Bush to greet the Texas Longhorn brass band last Thursday. It is called the Hook ’em, ‘horns salute and suggests a pair of horns.
In Norway, it created confusion, as it’s a salute to Satan (heavy metal again).
In American Sign Language it apparently means bullshit.
(Thanks to Derek)
A commenter pointed out that the above picture is not correct, because the thumb should be folded over the nails of the turned-in fingers. Here is a better picture:
This comes from the site of K-Read Custom Promotions, selling a variety of foam (sponge rubber) hands. Minimum order is 100 pieces.
Carter also points out that there is a lengthy post on the topic on Language Log. There’s so much on Language Log that I don’t see it all nowadays. The article concludes, after citing email received, that all the linguistic information in the source is essentially incorrect!