The first National Currency issued was the series of 1863, also known as Original Series notes.
These notes were very ornate and in my opinion represent a high water mark in national bank note design.
On the back left of each note is the state seal representing the banks location.
Valuing these national bank notes you have to take the bank into consideration.
A very nice example of one of the notes can cost less than $2000 if it's on common bank in Massachussetts.
The same note but from a bank in Washington state and all of sudden it's a note worth more than your car.
|"The Baptism of Pocahontas"|
This notes back design is pretty dramatic... it's the highlight although a case can be made for the action scene on the front left. $20.00 was fair amount of cash in 1863 so it's not surprising that these notes didn't survive in same numbers as the $5.00's & $10's.
A nice mid-grade $20 bank note will run from $800 to $1200. A full range of values would be from $300 to $3500 for an uncirculated example.
The note shown from Denver is a lovely example with pretty hand signed signatures and bright paper.