This serial number on an old Jacob Bros. upright traces to 1907! Serial numbers are sometimes hard to find, but typically on American uprights and grands they can be found in a plate cutout like this, somewhere in the tuning pin area.
Even more interesting here are the dates etched into the plate above the serial number. In days gone by technicians would often write or etch the date of each service call. Hopefully 1930 was not the last time this piano was tuned!