PS Vita Blog: "An Assassin’s Creed: Rogue walkthrough reveals a neat easter egg in Ubisoft’s upcoming PC/PS3/360 game. A poster in Abstergo clearly reads “Assassin’s Creed: Rising Phoenix Coming Soon”.
Assassin’s Creed: Rising Pheonix has a history. Allegedly, an image leaked in early 2013 from Ubisoft’s Digital Arts division that contained the Rising Phoenix name and some concept art. That same year a Spanish retailer listed Rising Phoenix for an October release on PS Vita. Giving some validity to the previous claims, the same Rising Pheonix logo was then seen on a wall in Assassin’s Creed IV: Black Flag.
The only Assassin’s Creed game on PS Vita, Assassin’s Creed III: Liberation, was developed by Ubisoft Sofia. The Bulgarian studio assisted in the development of Black Flag and are the lead studio on Assassin’s Creed: Rogue."