The pirate and ninja champions of the League start the game with a cosmetic buff informing you of their position. There is no requirement to obtain this buff other than playing one of the below-listed champions:
Akali, Kennen, Shen and Zed - Ninja: "This unit is a flippin' ninja!"
Gangplank - Pirate: "Yarr! I'm a mighty Pirate!"
Miss Fortune - Pirate Hunter: "Yarr! I'm a mighty Pirate... Hunter!