Hello everyone,
I'm new to the forum and recently acquired a large estate collection that included many classic stamps.
One of the stamps was mounted in a Subad Stamps dealer card identifying it as U.S. Scott #28 (3¢ Green George Washington, 1856). While researching it, I noticed that the stamp itself appears to read "U.S. POSTAGE" at the top and "ONE SHILLING" at the bottom, which doesn't seem to match the dealer card.
I'm hoping someone here can help me identify exactly what this stamp is. Is it a genuine cataloged issue, a local post, a cinderella, a fantasy issue, or something else?
I've attached high-resolution scans of the front and back. Any information about its identity, origin, or approximate value would be greatly appreciated.
Thank you in advance for your time and expertise. I'm looking forward to learning from the knowledgeable members of this community.

