Surely this insults the definition of "coin", which must surely possess some level of fungibility, if not availability for general circulation. If you cast a si

Surely this insults the definition of "coin", which must surely possess some level of fungibility, if not availability for general circulation. If you cast a single circle of metal in some unique pattern for some arcane financial purpose, then ceremonially transfer it to someone who cannot pass it on (because no one would accept it) - you have not, properly speaking, made a "coin" have you? The treasury is authorized to print coins, not one-off government deficit-spending authorization medallions.