If you're getting a very unique signature I would go to a gunsmith and ask. I would bet he will recommend removing and stripping the wood, getting the signature with some type of ink or paint, and refinishing. I would worry about recoating the wood over the signature. Depending on the finish, certian other finishes won't bond or will soften the other finish. The writing could run or smear.
I'm not a gunsmith, but I do have a good knowledge of woodworking.