This letters better than anything I have tried so far, cheap pen, extra fine point, water based acrylic ink. Got a few miles on that bottle of ink, hard to read the label, it is "Speedball Super Pigmented Acrylic Ink".
I bought all my lettering stuff at a Hobby Lobby craft store in the calligraphy section. I am sure most other craft stores sell the same pens and ink.
Produces very fine lettering with a little practice. The best part, if you goof-up you can wipe off your lettering with a wet paper towel and start over. I seldom get my lettering just right on the first try.
I put a couple coats of Tru-Oil over my lettering after it dries to "lock" it in place.