It's an interesting subject. There are three or four such codes and mostly they are of the "leave nothing but footprints" nature. One however, ASLaN, wriggles and sidesteps on the subject and although it obviously doesn't much like the idea of leaving anything leaves it up to the conscience of the customer. ASLaN is now defunct I think, which makes it a bit unfortunate that it should be the one codified voice that says what it says.