A site administrator can schedule notices that are shown sitewide

[mlncn]

Without the scheduling, site-wide notices can be done by creating and placing a custom content block.

[mlncn]

Notification Message is one alternative.

Lindsay and Mike, though, seemed to think that the real purpose of this was an IRB requirement that content be removed from the site after a certain date.

Either way, it is not used currently, but this time-limited content feature would have to be defined in a separate issue if wanted.

[mlncn]

For more alternatives, see https://www.drupal.org/project/drutopia/issues/3404504#comment-15335916

[mlncn]

We ended up creating the Dismissable blocks module for Drupal to meet this need in a simple way for another project.

[mikefortun]

even a dolt like me thinks that's cool!