I've decided i will use BKP's as im not looking to sell the guitar, want it for life :)
Do you have the pen that he signed with?I ask because it might say what type solvent is used in the permanent marker.Also a sprayer would be able to test their spray against something drawn with the pen - other than whats drawn on your guitar.The last thing you want is to dissolve the marker with the solvent in the paint to seal it in.