Dear Santa. Please make coins signable. Issuer name and short hashcode to prevent Unicode fraud will be enough.
Having non-counterfeitable item, with effort it will be possible to turn these coins into modern-style money, not just an object of natural exchange.
The following will become possible.
Someone (hearthling or village) issues money with his guarantee that, then asked, he will exchange these "money" for some valuable goods, pearls for example, at fixed rate. After that, he have to be powerful enough to force other hearthlings (villages) to use his money. It may be due his major role in trade, or simply supported by military force. With latter, one can demand contribution in his money, which will lead not only to taxation and griefing, but also will force victim to establish economical connections with his conqueror. And almost certainly if some critical number of hearhlings will start using such money (just coins issued by some guy), their prevalence will become self-supporting, or at least will take less effort to maintain.
What it will definetely not lead to: universal in-game money. Establishing good-for-nothing-except-exchange-medium good in this game is almost impossible, that is for sure. Also it will not change game mechanics.
What it may lead to: monetaristic reasons to start wars; more physical influence of the "empire", not just stupid runestone with "subordinate to Great Rome!" on it; economic bubbles; becoming shark of Wall-Street as goal in game; creating dollar-like money (without support by goods) as one of the highest goals in game.
Why it might not work: with game's exponential economic growth, it can be just too hard to work this out.
Sorry if this english is messy.