Now you say that but, a couple of years ago I saw Ozzy Osbourne interviewed on British TV a clip was shown of a US TV preacher (dunno his name) complaining about exactly the same hand signal which the fans apparantly use at Ozzy concerts. I think he said something like,
"...and I saw forty thousand teenagers make the sign of the devil with their hands...", then he did the hand signal.
Maybe the concert was in Texas and they were all Longhorns fans?
Oops, sorry, I replied to the wrong post
And I did the same thing during Ozzy (and other) concerts during the '80s.
It's rather more akin to halloween than a profession of belief in anything.
Ronnie James Dio, arguably the greatest lead singer in the history of heavy metal, brought that hand gesture into heavy metal a long time ago. He stole it from his grandmother who said it was all about how you pointed it, fingers down pointing at someone it's to assist the evil eye, finger up like hw W is doing it is protection from evil. Of course in metal circles all it means is "Dio rocks". Then Britney Spears started throwing it and now it's just another wave.