As you may or may not know, according to Catholicism, Peter was crucified upside-down as he felt that he was unworthy to be crucified in the same manner as Jesus Christ.
Reversing or inverting a symbol is sometimes a sign of protest against what that symbol represents, it can be seen as extreme disrespect to the symbolism of the original image. For example an upside down national flag is seen as extremely disrespectful to the nation that the flag represents. However inverting the Latin Cross is about as evil as lighting a candle for Peter instead of one for Jesus.
If Satanists or anti-religion protesters want to disrespect or protest against Christianity they should adopt an inverted crucifix instead of Saint Peter's Cross. An inverted crucifix is highly offensive to Christians...
|Whoops! How did that happen?|
Side note: I wonder how fundamentalist Muslims would react to an upside down image of Mohammad? That's like a double whammy! =O
Okay, now that we have the fact that an inverted Latin Cross is lame and not at all an evil symbol--behold; here is a screenshot of the latest development for my Quake level is progress. The working title for the map is "Monastery of Abominations," the setting is an evil monastery...
|The beginnings of the Monastery of Abominations...|
What's that? You say my evil monastery is sporting Saint Peter's Cross? Why, so it is. Remember when I said that some movies and black metal groups use the inverted Latin Cross aka Saint Peter's Cross as a symbol of Satanism? Yeah, that's because in popular culture (read: common stupidity) Saint Peter's Cross is often viewed as evil or Satanic. Quake, like DOOM, is a game with lots of "evil" imagery in it, it's not campy but the imagery is more along the lines of pop culture evil than imagery inspired by what most people would view as actual evil.
My map is an homage to Quake and the imagery is, therefore, "pop culture" evil.
Footnote: Saint Peter's Cross is a much easier symbol to make in a 3D program than the Sigil of Baphomet or any other imagery inspired by Satanism.