Board Thread:General Coding Help/@comment-26966924-20160331181411/@comment-1757994-20160331212835

Browseitall wrote: Doesn't it simply send messages to the message walls of all users? Any text you put in MediaWiki:SiteNotice is displayed in a panel at the top of every page. If someone clicks the Dismiss link, it sets a cookie and hides the text.

SiteNotice works on any MediaWiki wiki. Message walls are a Wikia's attempt to replace Talk: pages.