Needlebar.com has a chart showing serial numbers against years. Serial numbers between 1,500,001 and 1,619,904 for Frister and Rossman were made from 1915 to 1920. I'm guessing in the latter part of that period by your serial number.
There were no serial numbers beginning with the letter O, and the largest serial number without a letter in front was 16.831.099, in 1899. Check your number and then see the link below.
Nowhere! Serial number apply only to articles produced in quantity, their purpose is for traceability and identification. Serial numbers are a very modern thing, a sure way of telling that you have a fake and not an antique.
under the slide plate above the bobbin case.
To determine what year a Brother sewing machine is you use the letter and first number, which indicate the month and last number of the year. Brother sewing machines have coded serial numbers. The serial number B25139839 could have been made any year ending with the number 2 such as 1982. The owner manual would have a year. There are currently no serial numbers that start with a B.
On the frame
The frame
Frame
On the frame
look on the frame
Check the butt or frame.
Look on the frame.
On the frame. It's on the steering tube
Frame and/or butt
On the frame
Serial number is on the frame.
look on the frame