Coinage - Marked

Many of the coins from the major cities, especially those of 1 GP value or higher, are often minted with a press which has the ability to impart a magical signifier to the coin indicating that the coin is authentic.
The magic is crafted in such a manner that if the coin is moderately damaged or looses more than 5% of its volume (usually through shaving) the magical signifier is destroyed.
When subjected to a simple Shalingra designed to detect the authenticity of the coin, the signifier will either glow standard colors for the city or sometimes even have rune mark of the city glow on the face of it for a few seconds. The shalingra works on all coins within about a three-foot radius.
Higher value coins may actually have locator magic placed on the coinage. Borez coins often come with this locator magic and each coin is serialized by batch. The Royal Treasury has the necessary information, heavily guarded, to use location spells to find coins of any particular minting.
Kraylin coins are minted for extra durability using their presses, each coin has the hardness similar to granite.