Neat! I've seen a similar system on Pelikan ribbons.
Probably, everyone knows this little trick, but to those who have started into collecting old typewriters, and don't know where to find ribbon replacements, here are a few items I wish I knew when I started: First of all, KEEP THOSE OLD SPOOLS--YOU'LL NEED 'EM!! Go down to an office supply store and ask for a cartridge to a dot matrix printer that's got a half-inch ribbon. After you've gotten the ribbon home to the typewriter, wind it until you see a diagonal line on the ribbon--that's the splice. Cut it there. About five or six inches into the ribbon, tie a knot in the ribbon if the old one has a brad or a knot in it. Fasten the new ribbon the same way into the spool as the old one went in. Wind it all the way and tie another knot about five or six inches in also. The knots work the reverse mechanisms in most typewriters. Not all machines need the knot, so pay attention to see if there are trip arms beside the spool cups in the typewriter. If there are, you'll need the knots. Otherwise, if the trip mechanism is underneath--such as what Royal uprights are equipped with--you won't need the knots. Most Remingtons and Underwood new styles don't need knots either. Well, I hope I heyulpt (like the little girl on those old Shake & Bake commercials).