In 1959, Soviets Littered the Moon With Tiny Metal Pennants
Ten years before Americans set foot on the moon, the USSR intentionally crashed their Luna 2 probe into the lunar surface. It was the first human object to reach the moon. It also provided a simple but important scientific finding: the moon has no magnetic field. This crash-slash-success happened on September 13, 1959.
Beyond that science mission, Luna 2 carried a political payload. Inside the probe was a ball made up of pentagonal Soviet pennants, each a little steel plate engraved with "USSR January 1959" (the former two words rendered in Cyrillic script) and the USSR Coat of Arms. The ball had an explosive charge inside, which went off upon landing. This, in theory, allowed the pennants to break apart and litter the moon's surface around Mare Imbrium (the landing site). When Khrushchev visited the US, he gave Eisenhower some replica pennants.
It's unclear whether the moon pennants survived the Luna 2's crash, because we've never returned to Mare Imbrium to check (and they're tiny, so an up-close examination would be necessary). It's likely they were destroyed on impact. The success of Luna 2 was a blow to the American space program; the closest we'd gotten to the lunar surface at the time was with Pioneer 4, which only got within 60,000 kilometers of the moon and remained in orbit.
For more on Luna 2's pennants, check out this Objectivity video, which shows off replicas:
You might also enjoy this contemporary newsreel narrated by Ed Herlihy.
If you liked that story, you'll love the time Luna 15 crash-landed during the Apollo 11 moonwalk. Also notable is this massive list of stuff humans have left on the moon.