I continue to be amazed at the number of US branded zithers. This fine example, from Chicago, lists M. Kraus as the maker. Unlike the typical concert zither which has 32 strings, this maker has added a number of additional contrabass strings. The maker's label reads: M. Kraus / Maker, 1205 N. Halsted St. / (Patent Applied For) / Chicago.

She's a real beauty.

As for the "patent applied for", many people have used the phrase "patent applied for" and "Patent pending" phrase to ward off competitors and copy cats. He might have applied for a patent on the instrument or some element of the instrument. Then again he may not. As a competitor you would not know. The practice continues to this day. Presently in the US, the phrases, "patent applied for" and "Patent pending", serve as a public notice that an application has been filed with the US Patent and Trademark Office and the law imposes a fine on those who use these terms falsely to deceive the public.