Thanks for all of the responses guys. Lots of ideas there, I just wish I had a spare one to practice on first. I'd like to do my Xenon as well but I haven't been ale to track down the apron decal anywhere. If I did a practice run on one I'd be a lot more comfortable.

 

Depends on what it was signed with.. wet method is only water with the tiniest drop of detergent added.. nothing to dissolve ink unless its water based.
Personally though, id be giving it a quick spray with acrylic clear ( very thin coats.. leave to dry and then another very thin coat).. that way you can apply decal knowing its protected. This will also prevent any wear to the signature

I had thought about giving it a clear coat to protect but I had thought that was probably better done after the decal had been applied. I've reconsidered that though once I thought about the possible issues with the signature bleeding. He used a silver marker to sign with.