Where's the popup/warning when entering a forum mod?

I'm going senile. I know there's a mod around there that'll popup a warning message when you click on certain forums - for example, I want a popup that directs people to my classifieds section rules each time (or once a session) that they click that forum link.

I saw it about two weeks ago, thought "hey, I really need to install that at some point", and now that I have a few minutes to get to it, I can't find it.

Getting old sucks. If someone can point me to it, Boofo will wax your car.*

*this is a lie