The Great Serpent ring is an item of organizational regalia worn by Aes Sedai and their upper class of students in training, the Accepted. It is a golden ring fashioned into the shape of a serpent biting its own tail, an ancient symbol of eternity and time itself.
The Great Serpent ring is awarded to any of the novices who pass the qualifying test for Acceptance, and thus the Great Serpent ring is one of the most obvious ways to differentiate between a novice and Accepted (the more ornate dress worn by an Accepted is the other). Strictly speaking, an Accepted may only wear the ring on the third finger of her left hand.
When a candidate for full sisterhood is raised from among the Accepted as an Aes Sedai, she may wear the ring on whatever finger she chooses, or not at all as circumstances may warrant. The wearing of the Great Serpent ring is recognized as one of the most outward identifiers of an Aes Sedai by society at large, along with the 'ageless face.'
An Aes Sedai may use her Great Serpent ring as a signet ring to seal a letter and mark it in wax, as Moiraine Damodred was observed to have done.
Additionally, the Great Serpent ring is also awarded to women who were merely trained in the White Tower, who are free to wear it as a sign of her Tower education. Queens and Daughter-Heirs of Andor traditionally wear a Great Serpent ring if they had trained in Tar Valon, and do so openly.
Women who are put out of the Tower for failing the test to be raised to full sisterhood are permitted to retain their Great Serpent rings. However, if one such woman is apprehended masquerading as a full sister, her ring is confiscated and melted down.