Both should be banned, once an inquiry has been carried out. The player from matches. The brand from having it's logo displayed on equipment used in the professional game.
And I'll admit, I'm no shining light. I've unintentionally commissioned illegal bats to be made and seen them used in professional matches. Hence why I'd suggest a warning system, there are lots of laws some of which are confusingly worded (the MCC have to take a small part of the blame for this!). But I'd never knowingly produce an illegal bat or knowingly allow a player to use an illegal bat under my brand.