It would be silver coins, with the value of Pi - so everything must be valued a multiple of Pi. They would be produced by lost wax casting and have a specific weight, to be measured each time they are spent. If a coin comes up light when weighed, it must be used to purchase an actual pie - which must be eaten in its entirety immediately and broadcast on live TV, at which point the coin is remade with the correct weight.
They will be made with an ass on both sides (a human butt) and are to be referred to as "shits".
In conversation:
How much is my bill?
Six shits.
That's outrageous, I wouldn't give 5 shits for this meal!
I'm authorized to come down to 4 shits, but then I'm out of shits to give.
Fine, this load of shit has been weighing me down all day. And an extra shit for your efforts.
Thank you sir, I'm glad you had an extra shit to give.
I know how it feels to have shit in your hand, and you deserve it.