I took A1828 apart again to confirm it's a Mk 2 (more on that next post), and I tried to use a crayon to fill in the engravings. I suspect there's too much oil on the gun for the wax crayon to stick, so I started cleaning the finish off. I don't know if it was the denatured alcohol or the scrubbing, the following marking appeared in the remains of the painted finish:

Attachment 110392

I can't tell if it's anything at all, but it vaguely looks like 4 numbers or letters. Not sure if it means anything, but I tried to enhance the photo to pull them out a little more.

If it's just marks, feel free to ignore.