Oh it's anything of scandalous... Just stupied!
In Italy when a woman "sleeps" with another man that is not her husband... Well we say that her husband has horns and we do what Laura Bush did today...
In the most of cases just for jokes...
Can you tell me what's the meaning in America?
In most of the rest of the country(and I believe also in England), it is the "Devil sign" and is often seen at heavy metal concerts.
I think you described what the hook-em Horns sign means in Italy. In American, that's just a sign of support for the University of Texas at Austin athletic teams. Horns represent the long-horned cattle found in Texas, of course.
This other sign was something offensive. It was not good but no one would describe what it meant.