Series 1890 and 1891 Treasury or coin notes were issued in
denominations of $1, $2, $5, $10, $20, $50, $100 and $1,000.
A $500 denomination, with a portrait of Gen. William Tecumseh
Sherman, was authorized and a plate was made but only a proof
impression of the note is known and no $500 denominations were placed
into circulation, according to Paper Money of the United States
by Arthur L. and Ira S. Friedberg.
Treasury or coin notes were backed by metallic reserves, according
to the Friedberg book. That means the notes were redeemable in actual
coin, but where the silver or gold coin was to be paid out was left to
the secretary of the U.S. Treasury to decide.
The Series 1890 notes feature elaborate engraved designs. In fact,
the $100 denomination in the series bears a nickname of
"Watermelon" because the large zeroes on the back of the
note resemble watermelons. Taking it a step further, the $1,000
Treasury notes in the same series are known as “Grand Watermelon"
notes for the same design feature on the back, combined with the slang
expression "grand" meaning "1,000."