@Shog9 We are planning on having an experimental tag cleanup weekend on Super User this coming weekend. Could you look into it on its meta and maybe arrange to have a system message put up there during that time (and maybe during future tag cleanup weekends)?

That's not an event that requires a system banner. And that's what the sidebar bulletin is for.

@damryfbfnetsi What random said. Ask a moderator to schedule an event - that will not only show up on nearly every page of the site while the event is in progress, it'll show up before the event starts, with a link to the post documenting the event and an indication of when it'll begin.

Plus it'll go away immediately when the event ends, which might be kinda handy as well.