The NeoGAF user (goldsoundz) who spotted this says it's in an area of Shreveport commonly used for filming movies. Other GAFfers pieced together that it's probably for an upcoming movie called Battle: Los Angeles, which is produced by - ding ding ding - Sony's Columbia Pictures. The picture's release date is February 2011.
So, this Resistance 3 billboard would be an advertisement in the film, suggesting that 2011 is when the next Res is on the way. Check out the larger size pic:
The full uncropped pics taken by goldzoundz are over on NeoGAF. Note also the Resistance 3 logo - and the Statue of Liberty forming the vertex of the A. I guess the Chimera are going to lay waste to New York.
I've emailed a press contact for Insomniac Games to ask if they have any comment. Should any be given, I'll put it here.