In rock that symbol has always represented the devils horns.
or "i enjoy heavy-metal genre sound composition"
or "loud, fervent guitar playing pleases my ears."
i get your point, and in retrospect mr. Cooper may not have been wise not to have arranged his fingers in a way that certain people would find fault with, but on the other hand (though i can't pretend to speak for him) i am quite sure that he was not meaning to indicate his allegiance with the illuminati or his servitude to the prince of darkness.
my assumption is that it was meant to be more to the effect of
"the style of music with which i am associated with and enjoy skillfully playing is akin to what is commonly known as 'rock and roll' and i would like by a simple hand-gesture to indicate a comaraderie with all of my listeners whose tastes are similar"