Hey ! What do you think about making drawings are writing kind messages on coins, so that these are as widespread as money ?

Some countries regard vandals on their respective legal tenders as a violation against the property of the state...

I've just removed the oxidation on a part of the coin, that's no vandalism.

Also, such currencies are still valid in Euro zone (Spaniards used to write on their banknotes)

Oh, I see. Well, those who CAN do this MAY do this~ but good concept though~

Vinegar saturated with salt is efficient, that's well known among the children having "little" chemist kit for Christmas.

You just have to apply it with a toothpick, then use a tissue and really properly wash with water.