Carbide Scribe
Marks hard materials including hardened steel, stainless steel, ceramics, and glass
I bought a cheap Carbide Scribe (2-pack for $10) just on a whim but have been surprised how much I use it for all sorts of stuff. It is great for marking holes in wood or metal. Quickly scratching your name or initials on a tool etc. Also great for picking at things because it is pretty sharp. Many uses and even the cheap ones seem to be plenty tough.
08/30/192 Pack Tungsten Carbide Scriber with Magnet, 2-pack ($10)