My friend Marty posted this picture today on Facebook; the Bixi rack at the Musuem of Civilization.
And then, not twenty minutes after I saw this, came the answer, from CitizenCycle. Apparently there's a bit of a foreign-exchange program going on at Bixi. To demonstrate that there are Bixis all over the world, these bike ambassadors are hanging out in the Bixi networks of various cities. Mystery solved! (And, I might add, it's a kind of endearing answer.)