The H with Carman Fluid Steel was offered about 1908

Iron Age, April 2, 1908
https://books.google.com/books?id=5U0cu_tHZy8C&pg=PA1139&lpg

Hunter-Trader-Trapper, August 1912
https://books.google.com/books?id=Uy7OAAAAMAAJ&pg=RA4-PA73&lpg

I've tried to find a Carman mill without success. Unless it's this fella
https://en.wikipedia.org/wiki/Edwin_Salisbury_Carman