Actually that sign comes from a Jewish tradition originally (as best we know).
Isn't that an Italian sign as well. Also known as the "Malocchio" or a curse of some sort, kinda like a "jinx".
There is a certain spell you cast on people. In Italian they call it the "malukes" [apparently an Americanized version of Italian malocchio, evil eye]. A person may get the "malukes" from bad eyes of someone who is envious of that person. The effect may be mild and yet people have been known to almost die of this evil spell. You feel very tired and restless. Many people get very sleepy and don't eat. Some become so ill that a doctor can't help them. The only thing that will take the spell away is prayers of a certain type. You must take an article of clothing with you when you are having the spell taken away. Usually a woman takes her brassiere. They also say salt drives away evil spirits. You may also hold your fingers in a certain way You usually have them horned. I have seen some of these things work. I don't know if it's true or not, but I guess if you have faith in something it will work.