Skullcoin! It's denoted in human skulls. There is a certain existing supply (eg the Paris catacombs), and there can be a steady stream of new coins being er, mined. It provides a way of providing for your loved ones after your death. It is hard to counterfeit. It acts as a convenient memento mori to all users. It's easily stored.
And the best bit? Monetary supply and total population are anti-correlated. The more people you kill, the richer you get! Instead of merely burning up fossil fuels to make more money, you are just plain killing people and harvesting their skulls. Great stuff.