In order to issue barter tokens you have to have an institute people trust

This will freak everyone out as well, but a person could strike coins
which legally contained any number of radionuclides. Personally, I'd
skip the gamma emitters and beta particles - although I can get that
stuff free for the shipping - but a couple crushed grains of an alpha
emitter like Americium 241 would effectively place a permanent - and
slightly different - tracer in EACH batch of coins and the mix could
never be duplicated. To validate the coin, one need only Geiger it to
a known list to get the date denomination and number struck in that
batch. They can't be counterfeited - and stolen coins would be pretty
easy to find as well.

Alpha particles aren't dangerous unless they accumulate in one's
thyroid glands and that can't happen from a coin. It has to be a
nearly pure radionuclide and it has to be inhaled or ingested in a
form that can bond to the thyroid.

Am241 is free. It's in every smoke detector in the state. You's want
a reasonable competent radiologist to batch and calibrate the metal
before striking. I know someone who can do that. :-)