Mystery blade

[Iliad]

Good Morning/Evening Atlantia
I shall attach pics of the mystery blade as it was when I got it, so you can see the tang for yourself. The only mark on the blade is that of 2 interlocked circles on each side of the raised bit on the back edge; you can just make them out in 2 of the first pics posted. I had wondered if they are marks of a vice used to hold the blade while shaping/sharpening. The blade was sharpish when I got it, but I have since improved on the sharpness; it is now a very dangerous weapon. I have no way of knowing if it is tempered or hardened, but it certainly proved much harder to sharpen than some other blades I have dealt with. Yes, it is flat steel.
Interesting thing about sharp weapons, whenever I show some of my swords, daggers etc to people and say "be careful, this is very sharp", the first thing they do is to touch the edge! A bit like a "wet paint" sign!
Brian