Those playing the inFamous demo will notice when they come upon the Empire City cinema that the "film list" contains Sly Cooper 4.
Sucker Punch has been rumored to be working on the stealth-action game since 2007, and this little bit of tease is either a thumb of the nose, an Easter egg, or an announcement of sorts. We don't know.
Maybe E3 will shed some light. One can only hope.
You can see the offending image of the Sly Cooper tease first-hand over on Joystiq.