I'm pretty sure that my 1934 Guild Stratocaster flat-top, which is signed by Johnnie Guild himself, is totally legit.
I've always felt guitars with artist signatures should be worth less, not more. I mean, heck, they've been defaced.
But that's jussss me. /:
Make that jussss "us". We're a minority.
Don't get me wrong, I can appreciate why someone would want (and cherish) an instrument legitimately signed by an artist they admire, even consider it an heirloom piece, a trophy, a joy... but I don't want a Sharpie scrawl on a guitar even if it does say "Bob Dylan" or whatever, I'm too OCD about instruments, and I don't buy/sell collectibles for profit.
Different strokes, of course. For instance, I admire John Lee Hooker a lot, always have, big fan, tons of respect for the man, been to the Boom Boom Room countless times. And I like an Epi Sheraton, too. But this kind of thing (attached pic) doesn't quite work for me.
I'm surprised anyone still gives out their signature in the form of an autograph these days.