I’m gonna say it’s a QC or other identifying mark from the band manufacturer, or from the company that provides paper to the band printing company. Since it looks like it says “500 M”, if I had to guess I’d say someone at the paper company wrote the length on the end of the roll to identify it.
Maybe I’m wrong, but I work in manufacturing, specializing in mass production of steel parts - and I see stuff like this all the time on steel coils, and you don’t throw away perfectly good parts just because there’s some handwriting on the material