Greeks and Turks have the same beliefs about the "evil eye", which can be interpreted to mean the jealousy or bad intentions of another. Their "curse reversers" tend to be ceramic or glass depictions of an eye.
In this clip from The Soprano's, Tony's squeeze, Gloria, gives the horns (jokingly) to the gorilla at the local zoo.
Dio had rejected his Catholic upbringing. He wasn't warding off the devil, he was promoting it. After all, the band's name is Black Sabbath. Jeez...
In the 70's, Italian President Giovanni Leone shocked the country when, visiting Naples during an outbreak of cholera, he shook the hands of the patients with one hand, and with the other behind his back, made the corna. This was no doubt a superstitious attempt to protect himself from the disease. However the gesture, which was caught by journalists and photographers, was considered especially offensive for the patients.
This website (you can get a fairly lousy translation of it at Google Translate) showed Italian president Berlusconi throwing the horns with impunity. I am certain that Italian death metal fans and others give each other the horns daily, without any thought of a curse being attached. How did this happen?
Well, basically, it's marketing. Deliberate and organized marketing.
This sign has been repeated so much in the media that people think it's normal to flash a satanic symbol as a sign of greeting. And our most visible vectors of mass persuasion, politicians and celebrities, have been doing the promotion. Most celebrities and other public figures don't sport a certain color necktie or pair of shoes at a public event without an OK from their "image consultant" so don't think this is just an accident.
And now the Pope, the so-called spiritual leader to over a billion Catholics, has been caught in the act. If anyone should know the origins of this sign, it's him.
How did we get so far gone that the Pope thinks it's OK to flash what is basically an Anti-Christ symbol? What next for his Papal majesty? Biting off the heads of doves?