My LP DC is signed behind the tailpiece, with a sharpie back in 2004 and never had any issues, mind you I bought the guitar purposefully to have it signed and dont play it that much
also might be an idea to look into those transparent film protector type products to save nail marks etc..
http://www.stringsbymail.com/store/oasis-guitar-armor-static-cling-finish-protector-oh-4930.html