If those Satanists had paid attention in Sunday school, they would probably realize that the inverted cross is actually the personal trademark of Saint Peter, the first Pope, and one of the most revered figures in Catholic lore. When Peter was martyred by crucifixion he was said to have requested to be crucified upside down because he didn't feel worthy of dying the same way as Jesus. As a result, many dyed-in-the-wool Catholics actually consider the inverted cross to be a more acceptable thing to attach to your tacky jewelry than a regular right-way-up one.
And there are seven other symbols that might surprise you. Link -via Gorilla Mask