If a wiki has a sitenotice, and if that sitenotice is pretty substantial it sometimes appears as the preview for a search result in Google. This is a bad preview, since it's the same for every page.
We should add the data-nosnippet attribute to sitenotices, to tell Google (and other search engines?) not to use them in their previews. We already use this for printfooter, so it's presumably uncontroversial to expand it to here.