I have this display case mark on both ends how
common or uncommon is that case

Well, I'm not sure Peter. I do see them on Ebay now & then.
And I have bid. But, I've never connected, they seem to go fairly high. ( for me any way ) Jack

no holes for bow on this one so it is salesman case for sure.

It's a worthwhile and uncommon item, and it's bowless like all the other Dueber display cases I have seen.

Peter, here is mine but as you can see it does have a bow.

It is an 18s and I would assume yours is too? Mine is hinged for both front and back. It looks as if yours is snap on.

Mike, the snap-ons were salesman display and the hinged ones were marked to the consumer. I have seen one like yours that was gold filled.