I had forgotten about that part of Dale's book, John. It does look like there are some similar chips with initials on center inlays shown there.

I wonder when they were made and if there were just a few companies making them.

To me, they look just as nice as what we have been calling crest and seals that are made of clay or clay composition. Maybe they are a later developed process that was more expensive and never caught on with manufacturers or buyers?