@KeimCNC, I have had a lot of luck with OraMask but I have read that the shelf liner paper works just as well.
Here is my method for masking: Best Masking Material? The smaller river signs in my most recent post are actually full color mdf that I painted in a contrasting color before cutting, so no masking needed.
Edit: this one was made from a piece of poplar with a couple different rounds of masking and painting, so masking can give awesome results if done carefully:
