I write on the removable label that goes behind the clear window in the tip with a laundry marker. I did sell a kite recently so I just told the other guy to turn it over and write on the back.

I stuck a sticky label from a label maker on my board with my name and number and "beer on return". It's right alongside the foot straps where it's unlikely to come off, and it can easily be replaced if it does. I know it won't stop anyone who wants to steal the board from removing it, but it does provide an incentive for anyone who finds it to return it.