As far as I'm conerned, pictures of people giving hand signals doesn't mean anything either way. It's true that satanists use this hand signal, but so do non-satanists, and for some reason that signal is sort of connotated with "bad a$$!" and "bad mutha fu##a!" and "hardcore, in-your-face!", it's equivalent to telling someone "you don't want to mess with me because I'm a crazy mofo!" or something like that. Hard rock and metal music conveys the same feeling, only with the way the music is arranged, and so that hand signal and that music compliment each other, so many rock and metal musicians make that signal. It doesn't mean that those musicians are satanists, it just helps them sell more records because people like their image. It draws on the feeling of power, and makes the signaler feel powerful, simply because people (at least, western culture) have been conditioned to feel that way when they give that signal. If you don't agree with the meaning of it, then you feel little and less powerful than the person giving the signal. If you agree with it, then you feel like you're on the same level as that person giving the signal. This type of stuff is as simple to relate to as any non-verbal communication like "hang ten" which means "cut loose" or "relax and ride the wave" or "have fun at what you're doing" or gang signs like "west side!" which symbolizes that a person likes the west coast of America more than the east. err, i guess west side isn't a gang sign. Most people don't know what gang sighns look like, like the crips and the bloods, so when they see someone making tose sings, it means nothing to them but "huh?". But to a crip gang member (who often makes crip hand signals), when he/she sees the bloods hand signal, he/she automattically feels a sense of resentment, anger, and hate for the person making the signal and vice versa.
show me a picture of Bush swearing an oath with his hand on the satanic bible and his other hand holding a real human skull filled with human blood, while dressed in a ceremonial gown with only one shoe on, wearing a noose, kneeling in the middle of a pentagram that's drawn on the floor, and surrounded by red candles that circle the pentogram or something like that. Then maybe you'd have something. (I'm betting he did do something like that anyways), but of course nobody would have pictures of it... unless they plan to blackmail him if he ever mentions his involvement in these activities and tries to convict other satanists in high positions who have done many illegal and hanus acts. I highly doubt that Metallica members have gone through the trouble of doing something like this though.