The upside down cross know as the Latin Cross has Christian roots. It was how St Peter was crucified. It was said that he requested to be crucified upside down because he felt unworthy to die as Jesus had died. It is also known as a Satanic symbol. It was first a Christian symbol though.
The upside down cross is believed to be a sign of someone who has lost his faith. Other people regard such a cross to be the cross of St. Peter. This is because it is him who was crucified upside down.
One of Christ followers, Peter, was martyred by being crusified on and upside down cross. This has become a symbol of evil and the anti-christ except to catholics who call it the Cross of Saint Peter (since they bekieve they magiked him into being a saint after he died) and, based on a single bible verse about the 'cornerstone' of Gods church also posthumously decided poor, weak screwed up Peter was their first Pope.