If you buy on .bomb or the United app, it will list it as "Polaris Business Class" on the flight reservation screen and again on the seat map screen. You can also look up the flight on the "flight status" page and click on "amenities", and you will see business class listed as "Polaris".

If you are on another travel website, it may just list as "business" so you have to look the flight up on .bomb.

Regionally, I think all transpacific flights other the ones out of HNL or Guam/Micronesia are Polaris, as are all transatlantic flights, and all flights to Brazil, Argentina, Chile, or Peru.