Yes, I am familiar with that, but two different grades of steel will etch differently in just the same manor.
There are two ways commonly used to forge an axe head out of two pieces of steel (or use a steel edge on an iron head), with the harder piece at the cutting edge.
One way is to fold the head in half around the handle hole, and forge weld the cutting edge piece in the middle. Done that way, only a small part of the harder edge steel is exposed, but it would not look like the above picture.
The other way is to forge weld the hard edge steel on one side, and punch the handle hole. Done that way, a wide piece of hard steel is exposed on one side, and a very narrow part is exposed on the other. The pictures above do not present enough information to rule this out.
Or, it could just be a hamon line on a head forged out of one piece and differentially hardened. I'd need a better look to be sure.