That was their slogan.

A "signature" and what I'd argue they're trying to say here - is something built into their product that you see and say "oh, that's apple." Up till now, they've had that, but never felt the need to say "this is our signature" - because it was obvious.

"Designed by Apple in California" is a slogan. I get what you are saying, but I disagree. The whole "Jobs is dead, so is Apple" idea that has been portrayed in the press warrants a response from post-Jobs Apple. This is it. Its in a very similar vein to the "Think Different" campaign actually.