Sandthief's Ring

The Sandthief's Ring is a ring that offer invisibility to the wearer whenever the wearer needs it. It is sold at the inn in Ulgoth's Beard for a quite hefty sum of gold coins. It's not known if the ring lasts an infinite number of using it or run out of charges and destroys itself in the process.

In-game description
"ring of invisibility: 'Sandthief's Ring'. Held by a master thief for the better part of a generation, this ring was put to bold use in the markets of Waterdeep. Working a crowd in broad daylight, the rogue would steal countless numbers of purses from the nobles, replacing them with bags of sand so the theft would go unnoticed. His identity was never known, but the name Sandthief was cursed loudly in its stead. It is rumored he retired, and now lives among the nobles he used to rob."