Nice note. I am not sure of your knowlege in chartered notes but it is reasonably common to see this 1938 BMO $20 in UNC.
The book value of your note is $300 in AU and $400 in UNC. With what looks to be a partial fold on the right side of the note I would value this one around $350. The serial number looks interesting yet in my opinion not enaught to add a premium.
Regards
Jason