How to send all account users a common message?

What is the desired functionality?

Have multiple user accounts on a standalone Octoprint setup and need to send them / post a message I want them all to see when they next log in. Email is not an option. Is there a way (inherent or via plugin) that enables a pop up window with that message that all users on that Octoprint will see?

There isn't anything built-in to the system for that, and I can't say I've ever seen a plugin that will do that. The closest thing to it would be my sticky pad plugin, that allows you to write notes from the navbar, but it doesn't automatically show. Another approach might be the fortune plugin with just the message saved you want to send to everyone in it's dictionary of phrases.