Polyurethane to preserve a signature
I upgraded to a used Gibson SG in incredible shape a few days ago. I got it from a guy that didn't know to much about the guitar but I was told it was an Iommi special edition. the price wasn't inflated because of the "special edition" or anything like that I just paid a standard used SG price for it. When I got it home and looked at it closer I realized that it looked hand signed (silver sharpie signature right below the bridge). I erase arched the special editions a found out that mine was not one. It was just a standard ebony body SG. Long story short, I haven't had it authenticated yet but I'm pretty sure that Tony Iommi autographed this guitar. So what I'm getting at is that I don't want to destroy the signature if it could be worth a lot more than I paid for it nor do I really want a guitar that I can't play. so I thought a solution would be maybe a coat or two of polyurethane over the signature to preserve it in case it is real. I just don't know if that would mess up the guitar or if y'all knew of a product that would be better to use.
Thanks for the help,