The blog "Think or Thwim" has a posting about "How to Hide An Airplane Factory". I'd heard the stories of Los Angeles area airplane manufacturers, that covered their factories with mesh that made it look like farmland, complete with houses and other buildings but I thought it was McDonald Douglas in Santa Monica, not Lockheed in Burbank. Regardless of who did it, this blog has some great photos.

Before:

After: 

You'll find more pictures on their website as well as an interesting tale (or urban legend) of Jack Warner (of Warner Studios) painting Lockheed with an arrow pointing to the factory on the roof of his studios so that the Japanese wouldn't bomb the studios by mistake. Who knows if that one is true though...