How would you go about designing a pre-mod pop-up?

To prevent spam on weekends and holidays, we put our community into pre-moderation which works well enough. It certainly prevents spam from hitting the public!

However, as y’all know the banner that says “Your post needs to be approved” is in the least logical spot and due to how invisible it is, we’re often slammed with duplicate or triplicate posts due to people thinking their post didn’t go through.

While I can’t fix the pre-mod workflow, I am contemplating building out some sort of pop-up that we turn on when needed that greets people when they visit the site and basically says “We’re in pre-mod. Post away, but all posts have to be approved before they go public” (but more eloquently). Chances are people will forget that pop-up by the time they post, but it’s worth a try.

But…. how? I have no idea where to start with this, but very badly needed.