Unless the sign is completely shaded, you might expect 3 to 5 years from Helmsman. To maintain the finishing looking nice, fine sand it every few years and add another [link removed by moderator] Tung oil is beneficial, but it must be reapplied on a regular basis since it dries out. Tung oil does not usually come with a UV inhibitor, which is a drawback. There is a product promoted for log home exteriors that promise to be superior. It's something I haven't tried yet. It's known as Perma-*****.