Tanis - Nymanthium Empire
When the Zarazen hand out bounties of gold, they hand out Empire Crowns with a red tinge to them. You can see them interspersed in the regular gold Crowns.
Whenever magic is used within 10’ of these red crowns any Zarazen within 100 miles is notified.
This is how they knew that something magical was going on in Iron Cliff when the call for reinforcements came from the Watchman posted there. The change is subtle and only about 10% of the crowns in circulation have the red alloy in them, however, any bounty given out by the Zarazen or any services purchased by the Zarazen are completely paid for with the red gold.
Whenever a PC uses or makes a transaction, there’s a 10% chance that any gold coins they receive are red gold. If there is a red crown in the batch, then a DC 20 Perception check can be made to spot it if the PCs are unaware of the existence. Otherwise, if the PCs know of the existence of the red crowns, a DC 13 Perception check allows them to pick out all the red crowns.