Brion's email reminds me that we sometimes use an icon resembling Adobe's A to identify PDF, which is very ugly for an open standard. FSFE's initiative welcomes design help to make their icons better, their maintainer told me: http://pdfreaders.org/graphics.en.html
Also, the Internet Archive brought up a proposal to "Create a visual format/style to include an archived link next to an external link". https://www.mediawiki.org/wiki/Archived_Pages
Nemo