A Hermann Clementz sold over in Europe for around +14k , in 2008 , I think , titled "Kain&Able" .
Keep plugging away @ it , dtpahrump .
Sigs can be hard to find , but sometimes are easier to get examples of in the country of origin of the artist .
An expert would prob. have to remove any backing mat'l from a frame holding a painting to authenticate any painting in question , so you might think about doing so (and photo-document the process along the way) or : you might also consider paying an Art Conservator to do so for you (depending on the conservator , they might let you photo-document the process) .
I'm submitting this for your consideration because Hermann Clementz would sometimes sign & date his paintings on the back of the canvas/paper .
Sometimes 2 sigs are better than one .
Food for thought , anyway .