I recently helped NEFF with the hybrid letterbox for their forest in Littleton, MA. The letterbox style clues are usually pretty basic and use trail names/colors, landmarks, simple compass directions, and sometimes steps/paces. This one is fairly representative:
http://www.letterboxing.org/BoxView.php?bo...oxname=Oak_Hill
(although having a photo in with the clues is a little unusual...)
Choi
one of the LbNA webmasters