Stamp blunder pays off.

• Position: AMERICANA

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...