The accepted mode of getting otherwise unobtainable information is to go visit the cranky old hermit living in the mountains. It's just the sensible thing to do. So, naturally, everyone takes their monthly excursion to the hermit's hovel to consult him on everything, from lock-jaw to lovesickness, necromancers to nasal viruses.
Now, if everyone's always visiting the poor old hermit, there's going to be an enormous queue... "Wellcome to the Hermitt's Hovele, Please Take Ye a Number and Have Ye a Seate" reads the sign outside the packed dwelling.
Imagine the poor hermit, having retreated into the mountains to escape this precise situation...
In one region of a forest, all of the trees are identical, down to the leaves and the twigs. If the PCs carve something into one of the trees, it could mystically propigate until it covered all of the trees, or could vanish since it was not carved into the one true tree.