Walking in swamps is particularly disorienting so I hang flagging tape periodically (biodegradable). Was thinking of using small permanent marker to identify each flag, but instead discovered the quipu knot coding scheme. May be useful for others.
http://cultureandcommunication.org/deadmedia/index.php/Peruvian_Quipu. I tend to use Letter-Number coding scheme that corresponds to labels on my pre-printed map, using number equiv for the letter.