Master Thief's Coin

The Master Thief's Coin is an object in The Sims 3: World Adventures, wherein it can be bought from a special merchant in Shang Simla for 750 ancient coins while having visa level 2 or higher for Shang Simla.
The object has no direct interactions of its own. The description does not explicitly state how exactly the Master Thief's Coin results in finding more ancient coins, but it is likely to be when picking up coin piles or when opening certain treasure chests.