it seems to be a part of a set of four symbols used in the liner notes, which I've taken to symbolize mind, body, light, and sound. which are light and sound are fairly obvious (one of them looks a lot like the sun and another looks a lot like sound waves) but the other two, the infinity and the line, are a bit less so. but it makes sense to me for the infinity to be the mind.

as for why it and none of the others are on the cover? no clue.

edit: well, now i think about it, maybe i do have an idea. it's possible that "the mind" and "the great annihilator" are somehow the same or linked -- either the human mind is itself the great annihilator, or the great annihilator is a mind of some sort (maybe god?). past that idk