"Tu, was du wilst" ("Do what you Wish!")

AURYN is a talisman from the novel Die Unendliche Geschicte (The Neverending Story), also featured in the movie as a mystical necklace referenced as "The Gem - The Glory". A double headed serpent biting its own tail, or two mythological serpents symetrically biting one another's tail form an oval yet are not intertwined, in the book. 

The ancient symbol of snakes biting each other, or ouroboros, is where AURYN is derived from. Various cultures contain the historical accounts of such a symbol. AURYN involves one serpent being white, the other black. One eye red, the other green. 

Given the complete version as the infinity knot or grief knot appearing as an intricate variation of the figure "8" infinity symbol, or sign of the ouroboros. Duality is what the two snakes represent. The dual nature of the two worlds, one Phantásien (Fantastica or Fantasia) and the other Reality. Also AURYN stands for the twin nature of the two snakes, and their mutual creation and destruction. 

There is an interior of AURYN, mystical with gargantual serpents as statues. One statue shining brighter than white, the other darker than black guarding the Waters of Life consisting of a pool serving as the exit from Phantásien. Bastian is refused passage due to his unfinished stories in Phantásien. 

Atreyu continues with Bastian's quest, allowing Bastian to return to his world, leaving Atreyu to finish his story, the Childlike Empress' story, and history. Bastian returns to his world after learning to love himself as he truly is. Only then do the snakes of AURYN allow Bastian to return to his world. 

More about AURYN.
This symbol is also called "The Golden-Eyed Commander of Wishes" by the Childlike Empress, who is the mistress of the symbol. The symbol has a certain energy which flows only through the Childlike Empress who grants those permission to utilize the amulet. 

Unless this power is granted, one is unable to influence AURYN. The amulet does differ from the inanimate object AURYN, protecting and guiding the bearer, showing to all that the wearer is the Empress's representative.Atreyu wore the golden amulet in his quest to save Phantásien . Bastian, left to rebuild fantasia, was left AURYN by the Childlike Empress. It was then that Bastian discovered on the reverse side this inscription:

The words "tu, was du wilst" ordered giving him the permission, to do what he wishes, whatever he pleased. 

Additional words of the Neverending Story through AURYN:

"In the hands of the Childlike Empress, AURYN displays greater powers even in the face of the Nothing. She releases seven spirits to serve her as she ventures across her tattered realm to find the Old Man of Wandering Mountain. They carry her chariot and provide a haven for Atreyu and Falkor within. 

Bastian christens the Childlike Empress with her new name. She presents him with AURYN; her only request being that he follows the instructions written on the back. While it grants him the power to make wishes and imagine more of Phantásien ( Fantastica), it drains him of his memories which are his only way back to his world. Bastian searches for the same obscure boundaries of Phantásien (Fantastica), only to realize it is within AURYN itself.