Rather than using Radeon RX 600 branding, it appears we're looking at a Radeon RX 590 instead. VideoCardz writes about the discovery of an entry in the database of the Eurasian Economic Union certification office that reveals PowerColor's upcoming Radeon RX 590 Red Devil. Not a lot of details, but it looks like the card has 8GB GDDR5 memory.
The certification is the latest step before a card reaches the market, so it's likely we're going to see the Radeon RX 590 launch in November.