Bark Bite, Pattee Canyon, Missoula, Montana

One of life's little mysteries: Why are there random small nails tacked into a pondersosa pine along a U.S. Forest Service trail?  I mean, it's not like anyone would hang a yard sale sign out along a cross-country ski trail.
And one would hope recreational folfers, skiers, and hikers would think of the Lorax and be more kind to the trees.

Any other ideas?