Is this a Civil War banknote underprint?

Maybe Russell or another obsolete expert can chime in. I picked up this curious proof recently and I'm trying to figure out what it is. The red rectangle is about 5.5" x 2". I'll post a close up of one of the years. Do these look like underprints for obsolete notes? What else might they have been used for?
Intrigued by all things intaglio.
0
Comments
I would venture a guess at being for a bond.
That does seem possible. The year dates are about the size of bond coupons, but I don't recall seeing any coupons like this.
What about interest bearing banknotes?