Errors in printing of stamps are rare, enhance the value of such stamps and make them collector’s items.

Last year, the U.S. Postal Service observed the centennial of one of the biggest stamp mistakes in history the “Pan American Inverts.”

The occasion was the Pan American Exposition held in Buffalo, N.Y., to celebrate the accomplishments of the 19th century highlighting achievements in industry, transportation, manufacturing and the arts. From May 1 to Nov. 2, 1901, the exposition was sponsored by the state of New York, the federal government and the Buffalo business community.

On opening day, the Postal Service issued a series of bicolored stamps commemorating the exposition. The new stamps featured the theme of transportation. A limited number of the stamp sheets, however, were accidentally printed with inverted stamp centers.

The one-cent depicted the steamship “City of Alpena.” The two-cent illustrated the train, “Empire State Express.” The four-center showed an early electric automobile.

One hundred years later, the USPS issued a souvenir sheet featuring reproductions of the “Pan American Inverts.” The sheet portrays a world globe on top of which is a buffalo and a lady holding the American flag. In the upper left portion is the inscription “The Pan American Inverts.” The three inverts appear at the bottom. Along the right side are four reproductions of special stamps that now are official postage stamps.

The 2001 souvenir sheets are available from the USPS Stamp Fulfillment Service. You can call (800) STAMP-24.