Do you have a scanner? if so, scan at 1200 dpi or 1500 and crop to that corner. It looks signature-like. It could also be an ink transfer from a printed album page or something written under the stamp in an album page. try flipping your scan to see a mirror image.
Thank you for your answers.No scanner, I add more photos I hope better.A friend of mine collector heard that in America famous print shop put brand in the top right. What do you think? Your opinion more competence.