Permanent marker works fine. I wrote my cell no. on my footpad of my board and it's remained there no probs.
Only problem is I was in Cape Town for 2.5 years, so my board now has a defunct ZA number on it

I'll just have to black it out with more marker pen and re-label. Looks a bit crap, but improves your chance of getting a lost board back ten-fold.
Just use a fine marker and don't write too small in case you do get some slight bleeding of the ink which may make your number illegible.