This gesture is the Satanic salute, a sign of recognition between and allegiance of members of Satanism or other unholy groups.
That's the definition of the hand sign according to link I posted previously. You don't have to be a Conspiracy nutter to see that there's something odd about all these people using this hand sign considering it dates back thousands of years. You got think to yourself well if they were all at a heavy metal concert it would kinda make sense, but heads of state, royalty... It seems a bit weird to say the least.