Mr Shave, May I assume you mean ceramic COATED as opposed to painted?
I assume this is older than the 40's because it has a similar shape to those of the earlier plates. It's definitely not stamped. Looks like the numbers are rivited on.
Mr K7, if you want to turn your friend on to this, by all means. Otherwise, I guess I'll try a local auction. I'm dumping my hubcaps and stuff, too. Simplifying, if you will. I'm keeping the hood ornaments, though. I still like them too much.
You could be very right about the broker thing. Quite nefarious, IMO...