In 1955, thieves stole four prized stamps—and more than half a century later, two still haven't been found. A dealer recently promised a $50,000 reward for each of the stamps, known as Inverted Jennies, the New York Times reports. A stamp library is also prepared to pay $10,000 to anyone providing information that leads to the stamps' reappearance. The 24-cent Inverted Jenny stamps, originally purchased at a post office in 1918, feature a Curtiss JN-4 biplane printed upside-down, the Times notes.
They're worth a fair bit: Experts put the value of another block of the stamps at $3 million. The four stolen ones came from the collection of Ethel B. Stewart McCoy, daughter of a Dow Jones founder. The FBI has investigated their disappearance, but details remain hazy. Two reappeared after the theft, one in 1958 and another in 1980. As for the other two, "it's possible (they) were innocently acquired by collectors decades ago who did not realize they had been stolen," says the dealer offering the reward. "With the passage of time, the heirs of those collectors may not realize they’ve inherited stolen property." (Read more stamps stories.)