Why don't you just write them on strips of paper you tape to the board or place next to the board?
If you use them when reading a chess book or writing down games, you will soon memorize them. Then, when you are ready, you can take them off and you won't have ruined your nice wooden board.
You do have to be real careful applying them but the results can be good. In the very worst case, vinyl letters can simply be peeled off if you totally screw it up. 
Most times you can get it very close and then rotate or slide it slightly if necessary. I just put a small thin piece of cardboard on top and then a little thumb pressure. 1/2" seems a good size; the smaller sizes are a little fiddly. You also need a small knife (Maybe they call it a stencil knife?) to pry the letter or # off the backing. I'm entirely self taught so how hard can it be?
Not a quick process, but due care will result in a professional looking job. Unless you put a sealer coat on top, you have to be a little careful with the board afterwards Still dust it, but just use some awareness. Have fun!
And of course, in line with notmtwain's suggestion, you can always put a rollup vinyl/silicone/mousepad board under the wooden board with the edge showing.
And of course, in line with notmtwain's suggestion, you can always put a rollup vinyl/silicone/mousepad board under the wooden board with the edge showing.
Thanks Baddog for the suggestions. The vinyl board trick will not work due to the wide borders on the wood board. But I think I will go buy the vinyl letters so I can peel them off if I don't get them centered etc. I am ready to leave the letters & numbers on the board all the time. It can dress up a board as much as distract from it if done properly.
Stencils and paint would be easy for you and look nice as well. You can buy very small inexpensive bottles of model paint from a hobby store that would work nicely.
I added notation to one of my boards(in pic), I used what is calle "water slide decals", just google those words, and you'll be able to figure it out. Also serach for "full alphabet" or "alphabet".(and I recommend ebay)
I have a wooden board I practice on and want to add the coordinates to it. What product do you use and what is the best way of applying numbers & letters to a wooden board.
I was at Michaels the other day looking and found some stick on letters & numbers but was unsure what to buy. Also if I make a mistake applying them (off center etc.) I may not be able to correct the mistake thus ruining my board in a way.