Not all themes and plugin are made equal. Additionally WordPress itself has a bunch of useful hooks that can we used to place notices. While they are too many to add to the options (we might add some later). You can manually enter those custom hooks yourself and place a notice where-ever you want. Here is a video example of add a site wide store closed notice.
This makes it possible to set a notice anywhere on your website. You can use hooks from plugin, themes or WordPress Core.