I don't understand the painted rock thing. It's a new trend in my neighborhood and hiking trails around here. People paint "motivational" rocks and leave them

I don't understand the painted rock thing. It's a new trend in my neighborhood and hiking trails around here. People paint "motivational" rocks and leave them for people to find. Things like "JOY" and "INSPIRE" etc, as well as "SMILE" etc etc etc. I briefly considered painting "demotivational rocks" and leaving those around as a counter-prank but ruled it out after realizing I'd have to actually collect and paint the rocks, though it was an amusing thought for a few minutes!