Wiktionary
n. A stamp to affix as proof that the tax due on the marked product has been paid
WordNet
n. a stamp that is put on an object to show that a government tax has been paid
Wikipedia
A revenue stamp, tax stamp or fiscal stamp is a (usually) adhesive label used to collect taxes or fees on documents, tobacco, alcoholic drinks, drugs and medicines, playing cards, hunting licenses, firearm registration, and many other things. Typically businesses purchase the stamps from the government, and attach them to taxed items as part of putting the items on sale, or in the case of documents, as part of filling out the form.
Revenue stamps often look very similar to postage stamps, and in some countries and time periods it has been possible to use postage stamps for revenue purposes.
Usage examples of "revenue stamp".
In 1765, it passed the Stamp Act, which required that every paper document-ranging from newspapers, to deeds, to playing cards--bear a revenue stamp purchased from royally appointed colonial stamp agents.
And you can look at the revenue stamp date, if you still doubt my story.
He went to the medicine cabinet and got a flat bottle with a green revenue stamp on it and a glass.