1862 Greenbacks. Comparison of a 5 Dollar Demand Note (upper image) and an 1862 Greenback issue 5 United States Note (lower image). Note the removal of the words "On Demand" and of the phrase "Receivable in Payment of All Public Dues". Also note the Treasury Seal added to the United States Note. - Wikipedia
1928 Fifty Dollar Gold Certificate FR-2404 - The gold certificate was used from 1882 to 1933 in the United States as a form of paper currency. Each certificate gave its holder title to its corresponding amount of gold coin. Therefore, this type of paper currency was intended to represent actual gold coinage. In 1933 the practice of redeeming these notes for gold coins was ended by the US government and until 1964 it was actually illegal to possess these notes.