I see people are still weighing in on the “watermelon rock.” If I may, there really is a simple way to address the issue. Common trail etiquette instructs hikers “if you carried it in, you carry it out.” This is a simple rule that applies to the most remote wilderness trail and urban parks alike, and includes paint.
Sure, that rock is shaped like a slice of watermelon. Oh look, there’s one shaped like a turtle! And there’s a ducky! And there’s Trump’s hair! Before you know it the whole park looks like a Loony Tunes cartoon.
There is zero reasons to take paint onto a hiking trail.
Take only pictures. Leave only footprints.
Michael S. Miller, Arroyo Grande