U.S.-Mexican border region Dopers: What's up with "Frontera" licence plates?

Living in Southern California, I occasionally see Mexican-owned cars driven up from Baja California. The licence tags on those cars almost always say something like ‘BC-MEX’ and also ‘FRONTERA’, meaning ‘border’. Are all Mexicans registering cars in the border region required to get that kind of tag, or is it optional? Does it confer any privileges with regard to crossing the border going either way?

Until someone who knows what they’re talking about responds:

I’ve had the impression (don’t know where I got it from) that la Frontera was some kind of governmental district - nope, don’t know what the U.S. equivalent would be - so that presumably, it would be issued based on one’s address and would assist law enforcement in, um, tracking down the vehicle if necessary (SWAG).

Facts? You want facts? Oh, uh, sorry.

See here for details. :smiley: