Our favicon is used in various places around the Stack Exchange (SE) network, to identify the site.
Currently, it's for main and for meta.
The problem I see is that these are awfully similar to those for Earth Science.SE,
which are for main and for meta.
The larger versions offer slight differences, but it's still hard to tell quickly which is which (power users on this site, did you guess right, even after some time to think about it?):
http://cdn.sstatic.net/Sites/earthscience/img/favicon.ico for main and http://cdn.sstatic.net/Sites/earthsciencemeta/img/favicon.ico for meta.
http://cdn.sstatic.net/Sites/spanish/img/favicon.ico for main and http://cdn.sstatic.net/Sites/spanishmeta/img/favicon.ico for meta.
Should SE visually distinguish between the two very different sites?
(Discussion on Earth Science Meta is here).