To US stamp collectors the 1876 Centennial Exposition was a milestone event for two reasons:
1. The US Post Office Department issued its first ever commemorative postal stationery to honor the event. These were 3c stamped envelopes, with the embossed stamp printed in either red or green on white paper. The US did not issue adhesive commemorative stamps until 1893, when it did so to honor the World Columbian Exposition in Chicago.
2. In 1875, the American Bank Note Company, under contract to the US Post Office Department, reprinted all US postage stamps issued up to that time, for display and sale at the Centennial Exposition. In all instances these so-called Special Printings are distinguishable from the originals, and in many instances they are much more valuable.
I know this has nothing to do with folk music, but I am a member of the New York Philatelic Bandits, a loosely knit group of people who enjoy both folk music and philately. We get together each March in Rochester, NY, for a pizza party at which we sing songs about stamp collecting. Weird, but true!