I've looked at an electrolyte system for etching graphics in metal - it only costs about $500 (trying to remember the name Max something). You create B/W art only (maybe grayscale too) on clear transparency. Cover your metal object with electrolyte fluid, place the transparency, clip the transparency onto the metal object with wired alligator clips to either end of the metal object, turn the machine on and using electricity and the fluid, you burn the image into the metal. This works for marking tools, personalizing keychains and things like that. Obviously Lithium258 is doing this with katana parts - which is cool. But as he states, it's relatively easy to do (and quick) if you have the right equipment.