Stamp blunder pays off.

The next time you buy postage stamps, you might want to examine them closely. A block of four U.S. airmail stamps from 1918 with a biplane mistakenly printed upside down was auctioned in October for $2,970,000--a world record for a stamp item. When the stamp was first issued, a sharp-eyed stamp enthusiast purchased a sheet of 100 and noticed that the plane was inverted. The collector immediately sold the entire sheet to a dealer for $15,000. The stamps were separated and sold off for a few hundred dollars each. Some four-stamp blocks were preserved, and these became the stuff of stamp-collecting legend. "I collected as a child, and this was the stamp of my dreams," says Charles Hack, the real-estate entrepreneur who won the auction. He says the stamps are "an icon of America."