In Sheveport Los Angeles there is a billboard that says “RESISTANCE 3” on it with a PS3 logo across the top. Apparently film sets are fairly common in this area. Some speculation suggests that this scene is for the movie Battle: Los Angeles which is being produced by the Sony owned studio Columbia Pictures.
The film is currently set for a February 2011 release date, so one could assume that Resistance 3 will be launching some where near that or at least in 2011. If the title is expected to release somewhere around that time period then you could probably expect to see Resistance 3 at E3 2010 which is still quite the ways away.