Since I'm writing a story that involves monsters, hunting, and the Catholic church, it only made sense that I did a little research on the matter. So for the edification of those writing on the subject, allow me to share what I've learned. Standard Disclaimer: I do not claim to be an expert on these subjects, what I share is merely the product of my intense research. I may be wrong and I encourage others to correct me and do their own research!
First thing's first. If you have vampires and the church, crosses are going to come up. So I need to dispel one of most common misconceptions and that is this...
Do you know what this is? If you answered "a Satanic cross" or anything of that nature, you, my friend, are misinformed. What you see up there is a Petrine Cross. Also known as the cross of St. Peter. That is, this isn't Satanic. Or evil. In fact, it's quite the opposite. See, St. Peter was crucified upside down because he didn't feel worthy to die the same way as Jesus. That means it a symbol of humility before God. Don't believe me?
Take it up with the Pope, man. He had it carved on his freakin' throne.
But it doesn't stop there. There's actually a whole slew of crosses, all with their own unique meanings and connections. Just about every saint in Catholicism has their own cross or at least a depiction of the cross that identifies them. Here's a few of the big ones.
That blue X? That's the Cross of St. Andrew! Famously utilized in Scotland's flag. And the T? That's Tau cross or the Cross of St. Anthony.
Turn that cross on it's side and you've got St. Philip the Apostle's cross!
Toss a few extra bars on there and you've got the Papal Cross, symbol of the Pope!
So you can see there's a bunch to learn about the iconography of Catholicism, and this is just the crosses! I could go on about this forever, but I think you guys get the idea.
Main Idea: If you're writing supernatural horror, an upside down cross is just a symbol that the author hasn't done any research.
Don't Forget to Do Your Research!
Keep your eyes open for my debut novel, The Paladin.