In Italian folk magic, the "Mano Cornuto" known in current times as the " horned " hand originally represented animal horns and was believed to protect against the "evil eye" by "poking" the attacker in his/her own eyes, thus breaking their ill intent towards you. Over the ages a hand gesture arose and was used to pin or impale ill wishes and drive them to the ground..
common usage the gesture was also used to reveal an unfaithful mate, which is a
later adaptation of the symbolism in mainstream Italian culture.
You can read more in "the Cimaruta and Other Magical Charms From Old Italy" by Raven Grimassi.
A self-published book .