Try a Permanent Marker direct onto board & Kite
If you want them removable for later resale,
For the board write on a plastic self adhesive label (kite shops may have these)
For the kite plastic self adhesive label or stitch in a small label

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.