While different religions generally do not share iconography, certain symbols, such as the hamsa, the hexagram, and the inverted cross, are used by multiple religions. Sometimes this sharing is a result of cultural diffusion; in other cases, it is coincidental.
The hamsa or Hand of Fatima is a symbol shared by Islamic and Jewish cultures. It is a stylized human hand, facing palm outward. It appears to have entered Judaism via Medieval Spain, which was ruled by Islamic people called Moors. Both religions use the symbol as protection against the evil eye.
The hexagram, a six-sided star, is used in Hinduism, Shinto, and Judaism. In Judaism, it is called the magen david, and represents the royal seal of David, an ancient king of Israel. In Shinto, it is called the kagome crest and often found on ancient shrines. In Hinduism, the symbol is called the shatkona or satkona. It represents the union of the gods Shiva and Shakti.
The inverted cross is used as an anti-christian symbol, particularly by Satanists. However, Catholics use the inverted cross as a papal symbol. In Christianity, the inverted cross represents the martyrdom of St. Peter, a disciple of Jesus and the first Pope.