I intended to letter it with enamel, but there was none at the craft store. Instead I chose a permanent paint pen. The paint pens were in a locked cabinet, so I asked for help opening it, and the woman I asked didn't have clearance so she went to get someone else. While I was waiting I figured out how to open the case, but I didn't do it because I didn't want to be rude. I selected a color called Brilliant Blue, which looked like it would match my rims. On my way up to the counter, though, I noticed that it was marked "flourescent" and that wouldn't do. So I got to break into the marker case after all, to swap it for black.
I don't know if it's clear in this photo, but the lock shank is so long that if you turn it sideways it lets the plexiglass doors swing out.
I'd started to refer to the car as "my eyesore" since the coat of paint from 2011 got really dull and wouldn't take a second coat without flaking. It was so dull that the doors had fingermarks from where I closed them with lotioned hands. That gave me the idea to coat it in linseed oil, but before I had a chance I found an old chunk of beeswax and on a hot day started buffing it onto the car (before and after, above). I am really pleased with the initial results. Right now it is coated with pollen, I think I can preserve the surface by washing it when it's cold out, then parking it in the sun once it dries off.