When I can, I use an ECE machine to mark parts. One day I'll get a permanent plastic stencil made up with my company name on it. I made the temporary stencils on a small stencil blank pretty much like a mimeograph stencil. I keep an old electric typewriter to to make them. It's the style with the interchangeable wheel.....can't remember right off hand, Selectric maybe. I only have one or two wheels for it, and that limits my choices . I wish I could find some different fonts that were a little less plain. I can etch up to about 0.012-0.015 deep if I need to, and it doesn't matter if the material is hard or not, as long as it is conductive.
When I shut down the last QC dept the company ran, I collected all the steel stamps. I must have 25 sets, or partials. One day I'll sort them out and see what is actually usable. Some I know where used on harder material and ruined, so I will have spares on some characters, and shorts on some. Or plenty of spares for anyone who has lost a stamp. Who hasn't sent one flying across the shop? Or into the crotch? At least once the tears clear, those you might be able to find.
In a tight, I can freehand a stencil....that I kind of like, if I had any artistic ability. I tried tracing from a printed clip art once, and it actually turned out pretty nice. I need to drag all that stuff out and see what electrolytes I am short on.
ECE is something you might look into. Startup cost is not all that cheap, but versatility is fantastic, IMO. You can make your own stencils, as I do, or have a "USA" stencil made that is permanent. They are plastic, and are very reasonably priced. Also you can get a basic machine for pretty cheap. They are simply a low voltage power supply. You could build a basic one easily.