The 3c Postmaster Provisionals of 1861 have secured their place in history by being a part of the Confederacy during the Civil War.
At the time the United States Post Office and the Confederate Post Office found themselves in an awkward situation, where various laws created a confusing Post Office relationship between the U.S. government and the Confederacy. For a while, the Confederate Post Office simply paid their dues to the U.S. Post Office until they could gain control over their own mail system.
So to decrease the complication of the situation, the Southern Post Offices created their own provisionals, stamps issued for temporary purposes in local areas. Postmasters created their own adhesive stamps with their own elaborate designs. The stamps usually had the postmaster’s name, the town, and the postage rate. But some stamps also had very simple designs, like a hand stamped “Paid” or even a handwritten price on a small piece of paper. Other 3c stamps were adhesive.
Some postmasters even printed a value on the envelopes themselves, so that the envelope was ready-made to mail with Confederate rates.
These small pieces of history can still be found to this day, though it might be difficult to search them out.