Answer: The United Kingdom

If you’re a philatelist (a student of stamp history and likely a collector thereof), you’re well aware of this little bit of trivia. For the rest of us that just learned what a philatelist is, here’s a curious bit of stamp lore.

Every country in the world issues internal postage that bears a name indicating the country of origin, save for a single country: The United Kingdom. You see, adhesive postage stamps are a British invention and the very first postage stamps had no country of origin on them because the country of origin was obvious (they came from the place where all stamps came from). The image here is of the first postal stamp, the “Penny Black”, issued in 1840.

In the 1870s, when the Universal Postal Union was codifying various international mail rules, they granted Great Britain a permanent exemption to the rule of country-name-on-stamps for international postage because of the country’s contribution to the very act of sending mail. The only thing a stamp from the U.K. requires to serve as valid postage is a profile of the monarch.

So should you find a piece of international post on your desk with a nameless stamp, you’re sure to see the Queen staring back at you from beneath the postmark.