I guess it would depend on what you wanted it signed for. I think autographs would ruin a perfectly good looking guitar.
There are lots of people out there who idolize artists and would pay huge amounts of money for their autograph. So if you want to make money by making your guitar a collector's item, then go for it. However, if you still want to play the guitar - you have to be very careful that you don't lose detail of the signature etc., then it just becomes a guitar with graffiti on it, and may lessen the value of your guitar.
Great works are performed, not by strength, but by perseverance.
