You are asking questions and I am giving honest answers:
There is no way of finding out who signed the note. These notes were hand signed by one person (a nobody) who was hired to sign notes. These are not the signatures of the officials that are titled below them. Same nomenclature for the Federal Demand Notes of 1861. The Secratary of the Treasury and the Treasurer had more important things to do than hand sign notes all day, that is why the word 'for' precedes the title.
Despite your assurance of the note being 100% authentic, and an appraisal from a dealer (which amounts to little more than just an opinion), the fact of the matter is, that so far, this note is uncertified and therefore 'questionable'.
This note displays the boldest inkings (on both face and reverse) of any Confederate note that I have seen, despite condition, but then I am far from being an expert on the subject of Confederate notes. The inkings may add value to it, or may go the other direction.
I would strongly recommend that you get this note set in a
TPG holder from PMG, PCGS, or the like, which would serve to insure authenticity of the note and multiply it's perceived value many fold to any perspective buyer. "Then' submit to a large auction house.
If you decide against
TPG certification, I would jump on that $1500 offer without delay as I consider it to be very high for an uncertified Confederate note, despite the serial number.
It may be prudent to hold back on that victory dance of all the smiley faces until you actually have cash in hand.