As far an onboarding message that would be shown at signup I don't know of anything in the works for that right now. The closest I've seen in that area so far is that the official FAQ is supposed to be put in the menu bar on the right of the page.

Now beyond the signup message, there is a chat channel of #steemit.academy that has been working out materials to present and onboard charities. I've been working to gather or create materials for a more general, non-crypto audience...starting with college kids as my first target.

The closest outside of these was #projectnewbie (who recently went on pause) who would find and leave a comment on new users posts (usually intros) directing them to some FAQ's and the #steemprentice group to answer questions and provide help.

Feel free to DM me if I can be helpful on this for external, signup, and/or internal onboarding, definitely something I'm passionate about.