MediaWiki now natively supports page status indicators: icons (or short text snippets) usually displayed in the top-right corner of the page. They have been in use on Wikipedia for a long time, implemented using templates and CSS absolute positioning.
Basic wikitext syntax: <indicator name="foo">[[File:Foo.svg|20px]]</indicator>
Usage instructions: https://www.mediawiki.org/wiki/Help:Page_status_indicators
Adjusting custom skins to support indicators: https://www.mediawiki.org/wiki/Manual:Skinning#Page_status_indicators
Can have Chameleon these too?