Actually, that is not the serial number, but the charter number of the issuing bank, and it's something to get charter numbers less than 100, and for this particular one, that is the lowest charter number for the state of Wisconsin, so an added bonus. The serial numbers are located below the image of President Harrison and up to the right of "United States of America" so for that note, the serial number is pretty high, 115860, while the other note had a lower number of 92686, but both are still high enough not to add much to the value.