Can't believe how many people don't know this (and this is no offense to you, so please, take none).
I've seen this question on several bulletin boards, and can only assume none of the posters have been to Italy, or have never met Italians, either in Italy proper or anywhere else.
The "horns" are a curse/good luck symbol, still used in Italy to this day.
It's meaning can vary widly, from cursing someone to hell, or good luck, to its most used present day meaning in Italy, referring to one who is cuckoled- "sei un cornuto" (you are a horned one).
You see the "horns" (le corna) all over Italy, plastered on cars, key-chains, necklaces, etc.
Hope this helped
saluti