I agree that when 'rockers' make that sign, they are announcing a love
for 'heavy metal' (or at least they started that back in the '70s), and
yes, many of them were into satanism. But it also just became a gesture
used by fans who were mimicking the 'stars'.
Also remember that the fans of the Texas Longhorns make a similar
gesture. (hence the reason the Bush family does it).
there is the American Sign Language hand gesture for 'I love You' which
has the little finger up, the next two down, the index finger up and
the thumb out....making the letters for "I", "L", and "Y" all at once.
easy to find evil lurking...but don't throw Satan 'credit' when it's
not his due. If we listen to that video and 'watch people', then one
day or another, as my daughters, son, husband drives away, someone will
most likely assume I am 'throwing a satan symbol'...since I make the 'I
love you', then put my hand on my heart to say 'love' and usually put
my hand to my ear/mouth and make the 'call me' sign to let them know to
call me later when they get to their destination.