If I'm not mistaken, (I think it was) Blue Oyster Cult put the symbol to the heaviest form of metal on one of their album covers to signify that they played heavy music, but there are many people that claim to have used the term first.
Got Death Magnetic a day early!

The Low-Cardinal of Zeppelinism - If you're a diehard fan of Zeppelin, join Zeppelinism here

Winner of the "Biggest Led Zeppelin Fuck" award in the CR forum (2 years running!)