In previous discussions here, it’s generally considered that while some bands have a geniune occult internet, ones like this are mostly just doing it for show.
There’s no such thing as “selling your soul” as far as I’m concerned. Unless you mean, to other humans, where you trade your principles for cash.
The symbol on his arm is probably personal. It’s certainly not any of the Goetia… I’d recommend following up with interviews with the artist as he’s probably been asked about it at some point.
