A good ninja has no need for hiding, for no one knows of his presence.
Which reminds me of this one time I was playing... Faerun campaign setting. My character was a Drow Ninja, we also had a Drow Swashbuckler, a Drow Priestess, and a Near-Blind Underground Barbarian dood... The Ninja? Disguised himself as a (Fancy spoiled person posing as a mercenary to avoid attention), while it was the /actual noble-born swashbuckler/ who did most of the shifty, cloak-and-dagger hiding. :P