Here's DIN 16511 https://www2.informatik.hu-berlin.de/sv/lehre/korrekturzeich... for anyone interested. Perhaps someone in Finland could dig further? It might be a bit strange to have proofreader marks for proofreading marks, but maybe something slipped in.
"oikolukumerkit" found an image with more than just the DIN referenced marks, but not much more.
