I went to an art store and got a 'Soft Pastel' in white. It's like a soft crayon/paint stick. I smear it all over the sides, wait a bit and then wipe down the sides with kleenex. That leaves the pigment in the numbers. You might have to do it a couple of times as the pigment does stick to gether and might pull some out of the numbers. Also rubbing alcohol will dissolve it if you're not happy with the look.
That might work. I wish I still had that old crappy soft crayon thing from the red box (yeah, I had an original crayon from the box, believe it or not, when I got the box set second hand). Pastel might be the ticket - only problem, as they age, it'll chip out. At least Sharpie marks will stay on the die. However, I GET IT EVERYWHERE, ALL OVER ME, because I have stupid shaky hands. I can't figure this out, but I have some on my shoulder (under my shirt - what?!). But am I paying five bucks more for them to do it? No way. Honestly, only the D20 is the real nightmare. D8 and D10 and especially D12 for some reason are easy. D4 is a tiny headache, but not bad, and D6 is just bland. BUT I HATE ME SOME D20 PRECISION UNINKED DICE.
Love the equation (and the drawing at the end)! I always use just ordinary crayola crayons and they work just fine (though it's true that even ordinary crayon will chip out of the numbers with time, like the pastels).
I did use a black crayon on a clear GS D20, and it worked better than just one pass with an ultra-fine Sharpie (but not better than a regular fine Sharpie with the normal pointed marker tip). I think the moral of the story, though, is use what you like, but it's still gonna be a mess.The drawing at the end is a hoot - I found that online - it's originally something someone drew where dude with all the Fs around his head had rolled a 1. It's great since the other stick figure in the picture is just staring blankly at the mad guy. Awesome.