What does the rating in a message mean?

Solution 1:

By using the Orange Guidance Soapstone users can write and rate messages (both upvote and downvote). The score you see is the net score of all votes on that message. Up voting a users answer awards them 1 Humanity.

Normally users up vote messages if they find them useful, and down vote them if they don't think they are useful (or are downright false). Some users will leave messages such as "Good Luck!" for support, and users will normally up vote them as a show of thanks or as a way of showing the same support without placing their own message.

I believe that messages with a negative score are not displayed.