All Tendenci sites include the ability to put an emergency announcement at the top of every page on your site (assuming you haven't customized your templates to exclude it.)
This is what an emergency announcement looks like. In this case we used it to honor those who served on this Veteran's Day. The end result looks like the image below with the exception being that I added the yellow rectangle to make it more obvious what is in the emergency announcement versus the rest of the page. Keep reading after the jump to see how to add them on your Tendenci site.