I've been running a test: for the past 50 hours or so I've had the same six messages placed:
- "Praise the Sun" at the Sunlight Altar
- "Immanent amazing armor" where Armor of Thorns spawns
- "Be weary of demon" at Capra Demon fog gate
- "Need ring" at Four Kings drop
- "Try up" near a ladder that's easy to miss
- And "Try down" at the spot leading to the Great Scythe in Catacombs
And, you guessed it, NONE of them have been rated. Fifty fucking hours they've been sitting there. There's just no way.
My theory is that your messages don't get placed on your own server; that is, "your" Good Luck message has a 19 next to it on some other guy's server, but you'd never know it. That's the only way it makes any sense.
As to what happens when someone rates one, if we get the random humanity from when someone beats and invader, and we get the random extra estus when someone lights a bonfire, there's really nothing left for a rated message to do aside from giving full health like in DeS, but that's obviously never happened to me. :shrug