I do have a tan line where my watch wasI just returned from a beach vacation, and I took mine. However, it was kind of a waste of effort. I would not take it anywhere near the beach, so I only wore it in the mornings for my runs and then in the evenings for dinner. It was fun to have along, but it stayed in the room most of the time.
Even if you were away from the beach, I would not wear the watch while out in the sun. Wearing a watch in the sun gives you a really stupid looking tan.