"During wartime, Shigetaro Emura, the warden of Okayama Prison, aimed to rehabilitate well-behaved prisoners by having them craft swords"
I'm quoting from aoi Japan this year's description.
Mei type "E" - I posted 3 examples [Emura saku] have variations so even this sanji mei was done by different hands.
Reposting 4th one from older thread.