I think it might be less specific than a signature grape/blend, and more of a focused style or wine type. A region that proclaims it does cab, riesling, sparkling, and port-style isn't credible. It's a matter of brand credibility, because if your region is known for world class riesling, and loyal fans discover there are some warm spots that produce great cabs, you're ok.

When you think of Anderson Valley, what first comes to mind? Gewurz and Pinot. When you look closer, you find several other wines they do well there in that cool climate. Very credible.

In other words, you should be able to quickly do an association:

Napa: Cab
Dry Creek: Zin
Russian River: Pinot and Chard
Bdx: Cab blends

the = might be "rhone blends" or "german style"

To get a place in minds of consumers, you need an ="xyz" for the region and for the winery