Surprisingly enough, this minor artifact, though specific to an older joint campaign setting, works across various incarnations of D&D.
Signet Ring of the God-Emperor
The signet rings of the Elysian God-Emperor depict the holy symbol and seal of the emperor and empire. More so than any titles or regalia, they are the sign of his favored servants, for he entrusts the clerics wearing these rings with power over his own chosen people equal nearly to his own.
A cleric worshipping the God-Emperor wearing one of these rings may use it as a holy symbol. She may also use her ability to turn undead on Elysians, affecting them as if they were undead themselves.