In the comments on my answer to WendiKidd's question about a Canonical Post I recalled that during Private Beta we had a temporary "banner" across the top of the splash page, with a message encouraging users to participate on the Meta. This appears to be SOP—the most recently betafied site is currently displaying the same thing:
And I have a dim memory (or do I? it may be my own figment) that something similar was displayed on ELU during last year's elections to promote voter turnout.
It occured to me that if this could be made a stock component of all sites, editable (and suppressible) at will by the moderators, it would provide a means for communicating with visitors—particularly new users and our Learners, who appear to visit Meta only exceptionally.
It could be used routinely to remind users of any Preferred Practices which seem to be being neglected:
Be sure to upvote useful Questions and Answers!
If you ask a Question, give members of the community 12-36 hours to respond
Then, say “Thank You” by Accepting an Answer
Context, context, context! (It's easy to provide too little context; it's hard to provide too much)
If you don't understand an Answer, ask for clarification in the Comments
And it could also be used to advertise matters of temporary importance: what prompted the memory (and this suggestion), in the first place was a discussion about how to encourage Learners to give us more thorough feedback on proposed Canonical Posts.
LEARNERS: Help us help you better: review and respond to the featured Canonical Post.
I haven't been a programmer for 25 years, but it seems like it would be a pretty easy patch, particularly if the hooks are already in place.