That appears to be a sword knot, which was a heavy cloth or leaver band that a soldier (or more often a cavalryman) would wrap around their wrist to avoid dropping the sword if for whatever reason their hold on the grip failed. It's a bit weird in this context because the grip and quillion of the blade depicted appears to be a bayonet, which wouldn't normally have or require a sword knot. If you have more and better pictures, the fine folks at r/swords might be able to give you more information about the specific make and date of your sword knot.