What you have to do depends on what you mean by "ghosting". Sometimes it's a ridge of dirt dried into adhesive at the edge of the letters that doesn't come up with solvent and a paper towel. Sometimes it's fading or dulling of the vehicle finish around the letter that doesn't happen behind the letter. Sometimes it's polishes/treatments that were applied after the lettering that doesn't exist behind the letters. And more recently there are reports of paint discoloration behind the lettering. It's not fully clear what has caused this, whether something having to do with printer ink migrating through the vinyl to the paint, the adhesive itself discoloring the paint, or other cause.