Saw a new kind of California license plate, does anyone know what it is?

[NsXMas]

I saw a new BMW X3 with a strange California plate.

It had five digits (ie 15123), the left side of the plate had the letters D S T going vertically, and the right side of the plate had 9 3 D going vertically.

I don't think this is a dealer plate, but I guess I could be wrong. The car was in Arizona which is why I didn't think it could be a dealer plate.

Anyone know what type of plate this is?

 

[CDX_NSX]

If I'm not mistaken, it's a distributor plate. I believe auto manufacturer regional offices use those.