I'm going to make a long post again
Rich and I found out that some LNG's had a clear coat sprayed over the signature, and it did make it run a little. That was done in PA. Other LNG's were re-cleared. It definitely can be done. I would recommend a polyurethane, although they can yellow with age. On that color guitar you might try a water based polyurethane like minwax polycrylic. I tried it on a flame maple custom I made that had a water based aniline dye. That did NOT cause any reaction with the sharpie I use to line the inside of single coil pickup routs. (I like to make my single coil routs an "abyss" where you can't see anything in there
) There was already a clear coat in the pickup route because I stripped off a crapola finish that some car guy did for me. I didn't bother stripping the inside of the cavities, though, and it was clear acrylic car lacquer. So it went: lacquer-marker-polycrylic, and the only thing that I think happened was the color of the marker turned a little purplish black, but it did not run. By the way, spray cans have a higher degree of solvent in them.
If you decide to use lacquer, it will run for sure. BUT, if you spray a light dusting coat, even with something that is highly reactive to the ink, it should hit the signature "half dry" from the air on its way to the guitar. That helps a ton. If the lacquer hits the signature "wet" it will react for sure. If you spray a light dusting, then wait a day, and repeat for a few days, there should be enough lacquer on there to wetsand and buff. But don't think that because it's okay under there you can now lay a thick, wet coating over it, because the solvents will re-flow the previous coats and run the ink anyways. Each coat has to be light. Good luck.