United States Notes Part 3 - United and Par Value at Last

The 1870's (and in particular Series of 1874, 1875, and 1878) were a time in which the rainbow effects were done away with, though there remained significant red ink in addition to the red Treasury seal - decorations around the denomination spelled out, or around "Washington D. C." or in the form of red letters showing the dollar amount in Roman Numerals, "XX," "L," "C," "D," and "M" for 20, 50, 100, 500, and 1000 dollars, respectively.
This was also the time for the largest denominations United States Notes ever attain, $5000, and $10,000, equaled only by Gold Certificates and Federal Reserve Notes.
This was also the time that Treasury seals of any color than red make their first appearance, namely the green seals seen on 50¢ Fractional Notes of the fourth phase and 10¢ Fractional Notes of the fifth phase, and now the only color Treasury seals have, or have had for over four decades now, though Treasury seals of this color would not be seen again until 1929.
The United States Notes gets its name (I think) because, unlike the Confederate States Notes which lost all value (other than subsequent numismatic) after the Civil War was lost to the Confederate States of America, the notes of the North not only kept value, but were, for the first time as would ever happen with a fiat currency, come to be fully par value in gold within this period, namely by January 1, 1879. This was the United States truly backing even its fiat currency instead of merely printing more and inflating.