A fine example of the 1845-1846 5c St Louis Bears stamp is valued at $55,000 ahead of a sale at Robert A Siegel.
It will lead the May 31 Rarities of the World auction in New York.
The stamp is one of a rare variety printed on grey lilac paper, which is why it's expected to make more than the high four figure sum the 5c issue usually sells for.
The stamps were created prior to the introduction of the first official US Post Office stamps in 1847.
They display an attractive design based on the Great Seal of Missouri but were rarely used. Survivors are extremely rare.
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