“Leave only footprints
Take only memories
Leave no trace”
The entire “Leave no trace” is a catch phrase or mnemonic, not a syllogistic rule.
It is a stand in for “Reduce human impact to preserve and maintain the trail for the greatest accessible number of people” not a creed.
So, rather than requiring that you hold your breath on the trail (exhaling would leave a trace, after all) common sense and the plain meaning of the actual rule allows hikers to breathe.
The existence of the trail? That fits with preserving and maintaining the trail, as do blazes.
Shelters and campsites—those minimize over all impact. Human impact on the environment is reduced and the trail preserved for use by more people.
Graffiti on a shelter or the trail, well there is a reason that you can get federal jail time and a five thousand dollar fine for that.
“But the words,” this isn’t a linguistic “I win button” as the catch phrase has a long and well established meaning, with a class you can take on-line (and in a normal year goes with getting your tag!).
You want to establish a different meaning for some place away from the trail, give it a shot. But on the AT it has a clear meaning, with classes, trainers, etc.
The AT is different from other areas.
So on the AT you would not use a Dakota Fire Pit. In the south you will start root fires, in the north peat moss fires and in Pennsylvania you will rue your life’s choices (the rocks) or encounter ground water. Off the AT it might be a fine low impact decision.
On the AT you don’t build random cairns. That is because on the AT you will encounter them as alternatives to blazes. Adding them next to the edge of a cliff, etc isn’t art, it is just evil. Otherwise the forest service has rules against them.
Want more answers? You won’t get them from me, other than to hear me say “it’s a catch phrase”.
Pictures added for examples of “traces” (including someone who decided to spray paint over a white blaze).
Online classes and materials on leave no trace.