A small piece of adhesive paper that is put on an object to show that a government tax has been paid WordNet 3.0 & Open English WordNet

A revenue stamp, tax stamp, duty stamp or fiscal stamp is a adhesive label used to designate collected taxes or fees on documents, tobacco, alcoholic drinks, drugs and medicines, playing cards, hunting licenses, firearm registration, and many other things. Wikipedia

Adhesive label used to collect taxes or fees Wikidata

A stamp to be affixed as proof that the tax due on the marked product has been paid. Wiktionary

Stamp to affix as proof that tax due. Wiktionary (translation)

A small piece of paper bearing a design on one side and adhesive on the other, used to decorate letters or craft work. Wiktionary