link: The سیب, ایپل represents "forbidden fruit." It coincides with the scripture from Genesis at the very beginning "the fruit of the knowledge of good and evil." Because isn't this exactly what Bella ends up with? A working knowledge of what good is, and what evil is. Stephenie says she loves the beautiful simplicity of the سیب, ایپل and what it says to her:
choice.
link: The publishers chose it. As far as we, and Stephenie know, it has no meaning beyond looking pretty.
Eclipse: I don't believe Stephenie has actually stated anywhere what this one means. But the ones I've heard the most are: one end symbolizing Edward, the other end symbolizing Jacob. Each end representing her two choices of love یا the person she can choose to stay with.
Number two of Eclipse: One end symbolizing the vampire world, the other the human world. Bella's choice between the two. The lone still-connected string Bella's tie to her human life.
link: The chess pieces are a metaphor for Bella's progression throughout the entire saga. She began as the weakest (at least physically, when compared to vampires and werewolves) player on the board: the pawn. She ended as the strongest: the queen.