"Even a little kid starting to collect stamps knows about the upside down airmail stamp," Scott Trepel, president and owner of Robert A. Siegel Auction Galleries, told CBSNews.com's Lloyd de Vries.
"I think it's an exciting time in the stamp business, and I can't imagine offering a more exciting item," Trepel added.
In 1918, collector William Robey purchased a sheet of 100 of the first airmail issue, a 24-cent stamp showing the Curtiss JN4-H biplane, at the main Washington, DC, post office for $24, and noticed that the airplane was upside down. The clerk said he hadn't noticed, because he didn't really know what an airplane looked like, but he'd taken them back and give Robey another sheet if he wanted.
Instead, Robey kept the sheet and a week later, sold it for $15,000.
More than 90 of the stamps still exist, but there is only one plate block.
"Ordinarily, the plate numbers were trimmed off at the top on these first printing sheets, but in this case, because it was an invert, the plate number appeared at the bottom and was saved," said Trepel.
CBSNews.com's Lloyd de Vries reports on what
could be a record-setting postage stamp sale.
Sixteen years ago, it sold for $1.1 million, a record then.
"Now we're estimating that it will fetch $2½ to $3½ million dollars," Trepel said.
Trepel was the auctioneer in 1989, and would only say that the buyer then was a "Southern broadcasting executive" but it's not Ted Turner.
"I'm going to respect his desire for anonymity. I think he got his thrill owning the plate block and wouldn't get much of a thrill at having the world know his name," said Trepel. (But we had to ask.)
Siegel Auctions has beat the publicity mill for this sale, including displaying the plate block on display at a local jewel in East Hampton, the toney enclave for the very-rich at the end of New York's Long Island.
"It was fun to see the people bringing their kids in and looking at it. Ten-year-old kids were awestruck by it," Trepel told de Vries.
"I think everybody knows about this stamp."
And if they don't, they will if it sets a record Wednesday night for the sale of a postage stamp.
"We've had more interest in this particular piece, both from spectators and potential buyers than we've had in probably anything else I've ever offered," said Trepel.