Holy Ring

Holy Rings are golden rings of varying size worn by several Digimon; most notably Gatomon. These rings give the Digimon great power relating to their holiness.

Gatomon
Gatomon has been seen both with and without a Holy Ring. In Digimon Adventure and Digimon Adventure 02, Gatomon's ring gives her power the level of a champion; without it she is as weak as a Rookie level. She loses it sometime in between the first and second season trying to escape from a Unimon. It is returned by Gennai in the final episode.

Other Digimon
Several other Digimon wear Holy Rings. They can be anywhere on the Digimon's body, and they signify the Digimon is, in some way, holy.

Tapirmon's ring is on its leg; MarineAngemon's its neck; Salamon's its neck; Goldramon's its arm; Liollmon's its neck; Kudamon's its neck; Apemon's its finger; Hououmon's its legs (it has two); Rapidmon's its legs (also has two); and Lucemon's all its limbs: it has four.