As you can read at the very end of the Coinage Act a mill (written "mille" here) was instituted as a unit worth one thousandth of a dollar. Inflation has rendered this unit irrelevant, but for part of the mid 20th-century some states, including Missouri, issued "tax tokens" for when handling sales tax on small purchases. If something is worth 5 cents, its 10% sales tax of .5 cents, rounded up to the penny, suddenly becomes a 20% tax. Some independent businesses and smaller municipalities also created their tokens. So many were produced in Missouri, out of cheap red or green plastic, that they aren't worth much. Other issues were produced on paper or light metals.