You could do something like Village Tokens, of which each coin made in the village by the chieftain (or a lawspeaker) will embed a code into it that no one else can imitate.
But as is the current game only has coins for vending, so replacing that with tokens won't work because you'll have conflicts between villages.
So village tokens can be secondary set of coins but spent for that village... Think of it as ration tickets or something of which villagers can trade with each other, or with outsiders to let them spend it on stuff.
It basically can be held and traded by anyone, meaning you can sell your village's token to trade currencies between villages?
The one factor that really screws up currency, is the value of metal since it's very scarce in the game world...