Maybe figure out a way to phrase it positively--"You are encouraged to stay on topic"--something like that--rather than negatively--"Off-topic comments are not allowed"?
Good idea! I like positive.
How would y'all suggest distinguishing between posts that are OK-OT and not-OK-OT? Can anyone suggest any guidelines for determining whether a conversation has diverged too much from the topic? Or do you think it should be left up to moderators to judge -- with members obviously being able to contact moderators to express an opinion if they think a thread is getting too derailed?
The question is not disingenous. I think it is tricky to come up with rules about this. On the other hand, leaving it up to moderators does open the possibility for members to say the rules are being forced unevenly ("how come his/her post wasn't considered OT, and mine was?"). And enforcing the rules consistently across forums, as per brokeplex's suggestion, would be easier to do for if there were specific ways of determining where to draw the line.
What criteria could be used? Word count? Number of posts involved? How unconnected the comments are to the subject? Complaints from other members? Are there any ways to identify which kinds of threads that are more amenable to OT posts?
To get the ball rolling, here are some examples of topics I can think of where very OT comments might be a bit less welcome: games, Our Daily Thoughts blogs, perhaps TOTWs.
Let's hear your thoughts!