March 10 is U.S. Paper Money Day. On March 10, 1862, the federal government first issued United States Notes, following the passage of the First Legal Tender Act, signed by President Abraham Lincoln in February 1862. These notes quickly became the primary paper currency of the Union during the Civil War.
The front of a US $5 note, 1862
These were the first notes with a green back and were nicknamed greenbacks.
Back of U.S. $5 note, 1862