At least some of the generally unpopular Richard Nixon commemorative stamps are worth thousands of dollars.

An estimated 160 stamps were misprinted with the portrait off center and Nixon's name upside down, according to Linn's Stamp News, a newspaper for collectors.Linn's reported that an unnamed resident of northern Virginia purchased the misprinted stamps. It estimated the value of the stamps is as much as $8,000 each.

Such errors can occur when stamps must be run through more than one press to print a second color. If one or more sheets gets put in the wrong way the printing error occurs.

The most famous such case is the upside-down Curtiss Jenny plane printed in 1918. More recently an upside down candlestick stamp was discovered in 1986.

The Nixon stamps were first issued in April following a tradition of honoring former presidents in the year following their deaths. The stamps have not proven widely popular, however.