Several of the skins use the PDF icon when links to PDF files are in the content.
The PDF icon is however a non-free icon, http://www.adobe.com/misc/linking.html, and thus should probably not be used and shipped in the mediawiki software. A free alternative to the icon has been developed, http://pdfreaders.org/graphics.en.html, but in my opinion, the icon will be more confusing than useful to the readers atm, due to lack of recognizability.
A more generic icon might be the best choice for the immediate future.
Version: unspecified
Severity: normal