I could still do with some advice on engraving or some way to get really nice letters and symbols, so if anyone has any ideas, please let me know.
Here's some advice:
http://www.rolanddga.com/products/engravers/Don't buy one of the machines -- they're expensive, but do try to find someone in your area that owns one of these machines. Call Roland (the manufacturer) and ask if they know of someone in your area that has a machine of theirs that could accomplish what you need. In fact, get a few people, and then job it out and see what they can do for you in terms of price. Give them some subpar pieces to experiment on.
I agree with the people (fohat and others) who recommend starting with Esc for starting out with engraving. Those will sell the easiest in the beginning.
If I had an engraving machine myself I would gladly offer it's services, but, sadly, I don't.
Great looking work so far, and thanks for making some Buckling Spring stuff -- they needed some attention! Once there's an engraved set, I WILL be picking up an entire set.
EDIT:
My guess is that you would have to modify your mold so that more than one key could be engraved at a time; arranged in some kind of very consistent matrix, which, after engraving, would be broken away. But that's just my guess -- doing one key at a time would be mind-numbingly slow. Maybe you could start with an engraved WASD cluster?