RS refers to "reaction score"
Depending on how active a person is and how many people like the person, their messages (what you write IN the forums) count as messages.
And reaction score is how people react to you (only positive reactions count here.)
So having 0 messages (you are sticking to profile walls) and having 22 reactions that are positive, people love you! And having a 0-22 message to reaction score ratio is unfathomable and really hard to beat!