The inverted cross was NOT a satanic symbol originally.
According to legend, when St. Peter was captured by the Romans, they were gonna crucify him. But Peter asked to be nailed to an upside-down cross, because he wasn't worthy of dying the same way that Jesus did. So from that moment on, the Catholic Church adopted the inverted cross as a symbol of humility before Christ.
DISCLAIMER: I'm not trying to shove Christianity down anyone's throat. If you believe in something else, that's fine by me. I'm just sharing an interesting story about my parents' religion.