I know they are a "watermark" ... but I can't help thinking that they hurt you more than benefits you. First off, you're a writer, so your primary product is writing, so the maps are "promotion for your books", and you want people to enjoy looking at them. Secondly, YOU have the high res files, so should somebody copy your artwork AND remove a smaller signature in the corner (which most people wouldn't even bother with), you can always prove that the artwork is yours and people copying and spreading the work without removing the signature is actually promoting you This is of course my opinion and you don't have to agree at all, I'm only trying to help. I just know that in my favorite folder on DeviantArt you won't find any pics with watermarks on them, if I see a watermark I move on.