Well, thanks, gents. I knew about the match and felt tip tip

, but I'd forgotten about the carbide lamp trick.
There used to be a product called "Sight Black", a spray on, but the one time I used it it seemed a little more permanent than I want. Haven't seen that in years.
I guess the match would be the cheapest solution over the more expensive pen or the vastly more expensive lamp.
Dwight, I hadn't considered that flat surface. I think you're onto something.
Again, the help is much appreciated.