Hi David,

I have heard that the "little chain thingy" is used as an accessory to hold things together when a little too much weight has been acquired by the jacket's wearer!

It's less expensive than investing in a new jacket!!

However, that's not to deny that there might be a decorative reason for it on some jackets - although I have never seen it on a Prince Charlie (where the jacket remains undone anyway!)

Good luck in your search for info.