Extension:PageNotice

The PageNotice extension provides a way to create a fixed notice messages on the top or the bottom of
 * a page (by individual page name), or
 * entire namespaces (by namespace number).

You can define new fixed MediaWiki messages by creating new pages following a special page-naming pattern to hold that message, and then creating your desired message as the contents of that new page:

Usage

 * top notice for page XXX goes in  MediaWiki:top-notice-XXX 
 * bottom notice for page XXX goes in  MediaWiki:bottom-notice-XXX 
 * top notice for pages in namespace NNN goes in  MediaWiki:top-notice-ns-NNN  (where NNN is the numeric namespace ID)
 * bottom notice for pages in namespace NNN goes in  MediaWiki:bottom-notice-ns-NNN  (where NNN is the numeric namespace ID)

Examples
This will put the phrase: "Welcome to this wiki - you can edit every page!" at the top of every page in the main namespace:
 * Create New Page, name:
 * mediawiki:top-notice-ns-0
 * Create new page contents:
 * Welcome to this wiki - you can edit every page!

This will put a blue banner saying "Welcome to this wiki - you can edit every page!" at the bottom of every page:
 * Create New Page, name:
 * mediawiki:bottom-notice-ns-0
 * Create new page contents:
 * {| cellspacing="5" cellpadding="0" style="margin:0em 0em 1em 0em; border:1px solid #1DA0E7; background:#B3DDF4;width:100%"
 * |  Welcome to this wiki - you can edit every page!
 * |}
 * Result looks like this: