Found the following notice in the August 3, 1898, "Jeweler's Circular" on Google Books:

"D.Gruen & Sons, manufacturers and importers from Glashutte by Dresden, Germany, have removed their main American office and branch works from Columbus to Cincinnati, corner 5th and Elm Sts. ....They have also at the same time connected themselves with the Queen City Watch Case Co., for whom they will be general distributors of the entire product of hand made cases...."

I've found other references to Dietrich Gruen becoming the president of Queen City Watch Case Co., which apparently made expensive, solid gold cases. In 1900 there was a reorganization and a new corporation was created in Cincinnati named "Queen City Watch Case Manufacturing Co." with directors including D. Gruen and F.G. Gruen. They advertised "High Grade Gold and Silver watch cases and Special cases of all kinds.. "and our own specialty, Invisible Joints on Gold Cases." In 1921 the company name was changed to "Gruen National Watch Case Co."

This makes me wonder if Dietrich Gruen didn't decide to relocate D. Gruen & Son from Columbus to Cincinnati, Ohio, just to get control of a turnkey watch case factory. Has anybody ever seen a Queen City watch case? Did they make cases for Gruen & Sons watches?

From the lack of responses I take it that nobody remembers seeing a "Queen City" watch case before. Yet, the company was apparently in business for a couple of decades at least, and I have read that they had a large, modernized factory in Cincinnati around the time of WWI. One possible explanation occurs to me: If they specialized in fancy solid gold cases, maybe they all got scrapped/destroyed during the Great Depression.