I know of 8 of those unique pedestrians who show up as a blue blip "friend"
Tap dancing redneck
Paranoid war veteran
Zombie cosplay guy
Children of the Mountain woman
I've wondered for a while if finding every "friend" could trigger a secret final one to appear somewhere on the map.
As for the hippie painted water towers, well the aerial view of those towers matches one of the "connected circles" symbols painted on the side. Probably nothing, but interesting to note.