It has happened enough times that it may be possible to narrow down his customary days and times to hike the trail. If so, it might be possible to catch him in the act. Anyone who has a superzoom camera (or would like to borrow mine) could most likely get a good face shot from a long way off so that we could show both what is being done and who is doing it. If the friendly letter doesn't help, knowing that he will get a few thousand dollars in fines might do the trick. It might also be possible to find out who it is at the trail head. It wouldn't be someone in a large group because at least one person would probably have some sense. It would have to be someone with a fairly large pack since he probably carries more than one can of paint. If someone were to strike up a friendly conversation, saying something like, "Last week I saw some arrows someone has painted. It really helped me find my way. I'm hoping to run into the guy so I can thank him." If the person claims credit, then that's our suspect and all we have to do is get some pics of him and let him know that then next painting will result in huge fines. Perhaps even figure out which car is his and leave copies of the pics along with a friendly warning note. We don't want this to turn into a war of wills so that he starts marking defiantly everywhere, but we just may need some leverage.
z