I recently read a short story by Robert Heinlein called All you zombies. A couple of pages into the story was a reference to an insignia of a snake biting its own tail. I was just wondering if RJ was influenced somehow by this story or if it had a more significant meaning. 

http://en.wikipedia.org/wiki/Ouroboros

It's a known insignia. It depict eternity.... as explained in Barid's link. I think it served RJ well to describe the turning of the wheel of time and the ages repeating themselves. So the snake and the wheel work well together in that way.