I like US currency but will admit that my knowledge of it is not super strong. My wife's grandmother recently passed away and when going through her stuff her mom came across a few US notes. This appears to be a Pennsylvania 50 Shilling note dated October 1, 1773 (PA-170). The serial number is 26289. I know that Colonial notes have been reproduced and don't know if this serial is a known reproduction or original. I would love some information on this note, help to know if it is authentic, and what it is worth. Thanks.
Here's one very close to your serial number they're calling "28113" you can examine for authenticity: https://www.masshist.org/database/715. I can't publish the images of the sides as they're evidently copyright-protected but you can view them both by clicking on the image embedded in this link.
It appears authentic with brown (not black) serial numbers and appropriate signatures. It also has the correct red/black color scheme with some letters printed in 2 non-overlapping colors. The paper should not feel or look modern; it does seem to have some white mica flakes. Newman reference - it is 26289 of 28300 printed - 50s is the highest denomination of notes authorized 2/1/1773 and dated Oct. 1 1773 to "revive the Loan Office system."
