Deconstruction: Religious cult Symbols of The Devil Inside

The main religious symbol in The Devil Inside is what is known as The Cross of St. Peter. 
It is called this because Catholics believe that St. Peter was crucified upside down as he did not deserve to be crucified the same way Jesus was.
This symbol is also worn by a lot of Satanic followers because it symbolizes mockery and rejection of Jesus.
It also represented unworthiness and failure and reverence of Christ

In the film, this cross at first is thought to believe the original mark of Jesus, the Latin cross. When she carves these crosses into her arm you realise that from your point of view they are normal crosses, but from her point of view, they are actually St. Peter crosses. She also makes a similar mark on the inside of her bottom lip, which is obvious it is a St Peters cross.

These marks are also referred to as Stigmata (Greek word for marks) Paul talks about these marks in Galatians and many Christian followers claimed they did not know anything about what Paul was saying. But Paul was actually referring to when a person allegedly possesses marks on his or her own body, which Maria Rossi did.