No more speculation permitted until someone posts a pic of this curiosity!

Now let me break my own rule... my first thought was the previous owner repurposed a seatpost clamp as a kludgey lock ring mechanism for the headset. I have something called a Gorilla Lock on an old mountain bike that keeps the headset from loosening. Actually very effective although it should be completely unnecessary. The fact that other Sekine owners have seen this same doodad pretty much debunks my notion. Interested in learning what it does.