Tim Bray talks about how he can tell whether an asian person is a FOB (fresh off the boat) or not.  As a former-FOB, I know he is right.  In case he is still wonder, it is the primarily the facial expressions, body posture and the way a person move that gives it away more than the clothes.  My facial expression has changed drastically within a few years after immigrating to America.  When I shrug in Korea, they don't understand the jesture.  When I raise an eyebrow like Mr. Spock to express amusement or slight surprise, Koreans are often amazed.

The Faces of Asian Women. This may sound nuts, but I think people's faces reflect the language they speak. Perhaps because of my Pacific Rim base, I find this particularly obvious in the faces of Asian women. A huge number of the people here in Vancouver are of Chinese extraction, resident for periods anywhere between four generations and a few weeks. Being a normally male sort of person, I'm given to looking closely at women's faces. And quite often, when I look, I can tell instantly "she speaks generic North American English" or "she's a recent immigrant and has a heavy accent."… [ongoing]

There are inconsistencies though.  Once in a while, I get surprised when I see a person, whom I thought to be a FOB, speaking in fluent English.  This is the downside of using generalization and steotyping as a tool: you see what you want or need to see.