Actually i have seen many of these and i always respond . I call it african solidarity. It happens even to jungui had come with my other half sometimes back and i told her ill not take you to places you will see your bros and sisters. While walking near the uchumi on mbs rd pale southB we saw a white sister and she did the nod i was like you see even you guys do it while away from your own.
On another note i know of kenyans in Frankfurt they wait at the metro exit pale juu ukishamaliza escalator. Their job is to ask "wewe mkenya" of course when you look at them they know you are one

my mum was once shouted at from behind "umetoka jamuhuri?" in kyuk. akapenduka akasema "eeh!" the other fellows were very happy to find one of their own on pismo beach. needless to say the had lunch and talked kyuk to their heart's content. I have always loved talking swa abroad... hata kama ni mcongolese ama mrwanda, mganda mtazania or mkenya. it's priceless!

Enyewe I've also nodded.

But in some towns such as Worchester MA and Lowell, MA, you nod because you happen to be the only nigger who can't speak kyuk.