A rare stamp worth as much as $200,000 (£105,000) may be on an envelope sealed in a ballot box after the US mid-term elections, poll officials say.
Four "Inverted Jenny" stamps sold for almost $3m last year
Officials in Broward County, Florida, say they saw a famous "Inverted Jenny" stamp while reviewing postal ballots.
About 700 of the stamps were mistakenly printed in 1918 with an upside down illustration. Just 100 went on sale.
But it will be 22 months before laws will permit the box with the envelope to be reopened and the stamp checked.
The original stamps bear a picture of a Curtiss JN-4 plane, known as a Jenny, which was used for training pilots in World War I and later became an airmail plane.
'Oh my God'
Broward County Commissioner John Rodstrom told reporters he spotted the red and blue Inverted Jenny on a large envelope with two stamps from the 1930s and another dating from World War II.
"I thought: 'Oh my God, I know that stamp, I've seen that stamp before,'" said Mr Rodstrom, 54, who collected stamps as a boy.
"I'd forgotten the name. I just remembered there was a stamp with an upside-down biplane on it, and that it was a very rare, rare stamp," he told Reuters news agency.
The official said the envelope had no return address, and the ballot was disqualified because it gave no clue as to the identity of the voter.
The box containing the envelope was sealed before the stamp could be authenticated, and election laws do not allow the box to be reopened for 22 months.
In October 2005, a block of four Inverted Jenny stamps sold for $2.7m (£1.52m) at auction.
Maynard Guss, president of the Sunrise Stamp Club, told the Associated Press news agency that a cancelled [postmarked] Jenny would likely sell for $20,000 (£15,547) to $100,000 (£77,736).