From the Vaults of Xalishan:
Forged secretly by Rhaltros the Mad, the Silver Sigil is one of the lost artifacts of Xalishan. Appearing to be little more than a cloak clasp, the Silver Sigil was Rhaltros’s final trick against the Lords Council. The Sigil is fashioned to look like a snake biting its own tail, an apt depiction considering its function. The Sigil is sometimes referred to as The Mad Wizard’s Folly, as it was the last artifact he enchanted before his capture, trial and eventual executions for crimes against the Lords Council.
The clasp is little more than a trinket unless the owner knows what it is and how to control it. With a word, the wielder of the Sigil can call forth the magics within the device to imbue life into a corpse, which will then follow the commands of the wielder unquestioningly. These shambling creatures are mindless automatons, with no will of their own. They will follow any order, even unto their own destruction.
A shrewd wielder could command an entire army of the dead, which was Rhaltros’s intention. He wanted to use the device to raise a legion to destroy the Lords Council and free Xalishan from the grip of their laws. Unfortunately for the mad wizard, he was captured and the Sigil was lost before he could enact his plan. For over a thousand years it has been lost and forgotten, but perhaps it still exists, hidden away in the most unlikely of places.