This hand signed is commonly used by baseball players to remind each other that there are two outs in the inning. This practice was reportedly invented by catcher Elston Howard because the previously-used sign, an extended index finger and middle finger, was hard for outfielders to recognize from their distance from home plate.
The spelling "mano cornuto" is erroneous, the grammatical gender of the word mano (meaning "hand") is actually feminine (la mano), and the expression should therefore be "mano cornuta", to be pronounced /'mano kor'nuta/. However, the form "mano cornuto" is commonly found in English.
 As a sign of infidelity
The "horns" are often used to identify a "cuckold" which is, as the Oxford English Dictionary puts it "a derisive name for the husband of an unfaithful wife." The "horns" in this case refer to the behavior of the Tufted Cuckoo. (Some varieties of Cuckoo are brood parasites; that is, the females lay their eggs in other birds' nests where they are unwittingly reared: so the adulterer begets the cuckold's children.)
In contemporary Italy, the "horns" are placed behind someone's head, or explicitly pointed at a person (in Italian, fare le corna, meaning "to make the horns"). The conveyed meaning is that this person, usually a man, is a cornuto, a cuckold, bearing the cuckold's horns. The gesture is used with the same meaning in many countries: in Spanish-speaking countries (known as los cuernos, "los cachos" in Ecuador and Colombia), Portugal and Brazil (corno, cornos or chifre), Albania (briret), Slovakia and Czech Republic (known as paroháč), Greece (κέρατα), and Malta (kurnut).
In Cuba, Mexico, Italy and in Portugal, to place the corna on someone's head when taking a picture is a common childish joke (similar to using the V sign as "bunny ears" among Americans, or "donkey ears" in other countries), and young Italian tourists in foreign countries might be noticed looking nervously over their shoulders in group pictures. Italian prime-minister Silvio Berlusconi was seen displaying the corna on occasions, the most famous being a meeting where he put them over the Spanish ex-foreign minister Josep Piqué; this behavior caused some controversy in Italy.
This use of the shape of horns has been said to derive from the legend of the Minotaur, who was born from queen Pasiphaë's infidelity with a white ***, betraying her husband King Minos of Crete; the most prominent proof of the betrayal, the horned offspring, was taken as its symbol.
An alternate explanation for the origin of this symbol is that it comes from the Roman days in which horns were given to returning soldiers. They came to imply that the soldier had been victorious in battle, but not so with his wife (while he was away).
A third explanation is that, just like a horned animal cannot see his own horns but everybody else can, so a cuckold does not know his condition, but everybody else knows (especially in a small town).
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 of curses commonly known as ***ú, as well when a mention is made of someone or something it is 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. In Cuba this sign is used to indicate a man whose wife is unfaithful, and as of superstitions, 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.
The President of the Italian Republic Giovanni Leone shocked the country when, visiting Naples during an outbreak of cholera, shook the hands of the patients with one hand, and with the other, behind the back, made the corna. This act was well ***, as all journalists and photographers were right behind him, a fact that had escaped President Leone's mind in that moment. The gesture was interpreted especially as offensive for the patients.
Pointing the index and little finger at someone is a common Italian curse as well as an accusation of cuckoldry.
 American Sign Language
Made using a ombination of the letters 'I', 'L', and 'Y' from American Sign Language. It is made by extending the thumb, index finger, and little finger while the middle and ring finger touch the palm. The gesture means "I Love You".