The sign of the horns is a hand gesture with a variety of meanings and uses in various cultures. It is formed by extending the index and little fingers while holding the middle and ring fingers down with the thumb.
Some hold that when confronted with unfortunate events, or just when these are mentioned or suggested, a person wanting to avoid that fate could resort to the sign of the horns to ward off bad luck. It is a more vulgar equivalent of knocking on wood. Interestingly, superstitious ones can alternatively "touch iron" (tocca ferro) or touch their noses, which are not considered as vulgar alternatives, or (for males) grab their testicles (the left one with the right hand in Argentina, a country very influenced by the Italian culture), which is considered very vulgar, but is perhaps the most commonplace of the three. In Peru it is shown usually by saying contra (against). In Dominican Republic is usually used the expression zafa as a protection against curses commonly known as fukú, as well when a mention is made of someone or something believed to be involved with a curse. All of these gestures are meant to somehow conjure some supernatural power to protect the performer of the gesture. This sign may be used (e.g. in Cuba, Brazil and in Italy) to indicate a man whose wife is unfaithful (probably in the very widespread traditional association of horns with a cuckold), and as with superstitions, gestures to avert harm such as knocking on wood or saying "solavaya" are commonplace.
Such gestures are typically used when a black cat crosses one's path, when seeing a hearse (whether or not it is loaded), or when encountering any situation, object or person believed to bring about bad luck. It was once thought to prevent or distract the effects of the evil eye, that is of intentional or directed curses. Historically the gesture was pointed at people suspected of being witches.
In Italy, pointing the index and little finger at someone is a common curse as well as an accusation of having an unfaithful wife. With fingers down, it is a common apotropaic gesture instead, by which superstitious people seek protection in unlucky situations (something like touching wood). Thus for example the President of the Italian Republic Giovanni Leone shocked the country when, while in Naples during an outbreak of cholera, he shook the hands of patients with one hand while with the other behind his back he made the corna. This act was well documented by the journalists and photographers who were right behind him, a fact that had escaped President Leone's mind in that moment. The gesture was interpreted as especially offensive for the patients. It is much more common in southern Italy, and is typical in the popular culture of Naples, where President Leone was born.
During an European Union meeting in 2002, Italian prime minister Silvio Berlusconi did this gesture during a meeting picture. Asked why, he answered he did it "because it's fun".

en.wikipedia.org/wiki/Sign_of_the_horns

Satanic Hand Signs

Hand Signs1:Sign of Satan