I've got an Onyx Boox M92 device from ArtaTech
(to my regret, of course).
The front of the (black plastic) casing says: BOOX
The back of the (black plastic) casing says: BOOX, Model: BOOX M92, DC 5V - 1A, www.onyx-international.com
The only two places which explicitly say that it is the Boox M92 "Black Pearl" Edition are two small aluminium stickers (which also include something that looks like the device's serial number): one on the carton packing and another one on the warranty card.
Please note, according to the "official" web page with ArtaTech firmware updates
, they actually distributed TWO devices which they both call "Onyx Boox M92":
1. devices bought before 15th May 2012, which ARE NOT "Black Pearl",
2. newer devices are "Black Pearl" (aluminium stickers MUST explicitly say "Black Pearl").
I have no idea what the differences between these two "editions" are (they explicitly say, however, that different devices need different firmware).