The Curious Expeditions blog has a concise cultural history of the "evil eye." The short essay has lots of information I didn't know about this particular curse. From the blog post, titled "The Eyes Have It":
…The greatest modern protection against the evil eye was made through the work of an unsuspecting Italian American rocker, one Ronnie James Dio. Growing up in an traditional Italian home, Ronnie was accustomed to seeing the horned hands or "mano cornuta" displayed against the evil eye. All crescent shaped objects ward off evil (hence the lucky Horseshoe) and the horned hand (representing pre-Christian minotaur horns, not devil horns) was yet another way of warding off bad luck and the evil eye…
Ronnie James Dio's grandmother often deployed the horned hands and when Dio became the front man for Black Sabbath, he replaced Ozzy Osborne's peace symbol with the corna or as most of us know it, the metal hand. From an Interview with Dio at Metal-Rules.com
"It was symbol that I thought was reflective of what that band was supposed to be all about. It's not the devil's sign like we're here with the devil. It's an Italian thing I got from my Grandmother called the Malocchio. It's to ward off the Evil Eye"