A adhesive stamp attached to stocks, bonds, and other financial documents representing a small tax paid to either a country or state. In some cases, revenue stamps were attached to the stub instead of the actual certificate.

a stamp placed on goods and documents to show that the tax had been collected

A revenue stamp, tax stamp or fiscal stamp is a type of adhesive label used to collect taxes or fees on various items. Many countries of the world have used them, for documents, tobacco products, liquor, drugs, playing cards, hunting licenses and other kinds of things. While revenue stamps resemble postage stamps, they are not found on mail, nor do they (usually) receive a cancellation.