Last modified: 2011-03-13 18:05:32 UTC
I noticed when I attempted to clear out my Watchlist that [[Image:California state seal.png]] was a red link. Clicking the link gave me a blank edit box, but I tried going directly to the page and found that the image existed, it was simply hosted on Commons. Normally links to a Commons-hosted image's page on Wikipedia will be blue regardless of whether there's a Wikipedia addendum to its description, but on the Watchlist this rule apparently doesn't hold right now.
Such pages indeed don't exist unless you put something in them, so there's nothing for the watchlist to show.