"Just in case," I thought I'd mention that one of my Painter rifles was faintly signed with his initials, lightly engraved in very large, scrolling antique capital letters that were hard to see and to read due to handling wear. You've probably checked it closely already, but if there's any hint of lightly engraved lines, it might be worth another check. I wouldn't worry about looking under the barrel; if he signed it, it should be on top the barrel since that was their "advertising" back in the day.
Shelby Gallien