U.S. 1844, Dorothy Dix Regular Stamp, USPS Souvenir Page. First Day of Issue Sept 23, 1983, Hampden, ME 04444. Scan is an example. Never folded, shipped flat in a sheet protector.
USPS Souvenir Pages or American Commemorative Cancellations are -Official First Day of Issue Cancellations, which are a mint stamp or stamps affixed to an 81/2x101/2 color page, and include technical and historical information about the stamp or stamps and the designer. The pages were issued flat and unfolded.