I could be wrong, but I believe the masks are typically a symbol of "Comedy" and "Tragedy" when used in the context of theater. One masks is usually smiling and the other is frowning. The odd part is, with SymphonyX, the masks always have a neutral look. One of the masks has a tear drop painted on it, but it doesn't look sad. The other has lines painted down from the corners of the mouth, but again, it doesn't look sad. I'm not sure if they are supposed to represent the same meaning as the ones with the smila and frown, but I guess you'd have to ask the guys in the band what they mean (not Russell, of course, as he wasn't there when they were first used).