The Swan-shaped golden locket is a gift that Derek had given to the infant Odette as a present with his widowed Mother Queen Uberta. It has the form like a heart and at the middle of the heart it has a picture of a swan.
It is Odette's only piece of jewelry and necklance she wears throughout all five movies. She never takes it off or replaces it with another jeweled pendant. It is not known whether or not the locket itself possesses any magical poperties or any special abilities of its own.