What does the apple mean on the front of twilight?

Twilght: The Apple= the fruit of forbidden love

New Moon: The flower with the falling petal= the flower is Bella and the petal is the part of her that she lost when edward left her.

Eclispe: The broken ribbon= the ribbon stands for thhe love she has for edward and Jacob; the longer ribbon, of course, stands for edward.

Breaking Dawn: The white & red Chess peices= Red pawn stands for when she was mortal and the white queen stands for when she becomes immortal.