Punto's original paint should have been oven baked and lacquered, so unless the door has been resprayed, ordinary cellulose paint thinners should not harm it, especially if wiped off quickly.
The paint the yob used is hopefully cheap stuff. Get some thinners and try it on the stuff on the windows first, difficult to hurt the glass. If the paint comes off easily, it should do so on the door too. Then wipe it off the doors gently, wiping the thinners off quickly as it removes the graffiti. Should be able to remove it without damage.
Unless any body/paint experts have a better idea. So await further replies, but meanwhile, try to park the graffiti area out of direct sunlight if possible.
