But that's only for Orthodox Jews, and people don't just assume anybody's Orthodox, especially when they're wearing their hair out! Actually, I've never seen or heard of either of those motives for the question, if a Jewish person asks somebody if he/she's Jewish, it's most likely to relate, maybe commiserate, and share roots. It is a nice feeling. When a non-Jew asks, it's usually an ID thing - like what are you, Italian? No? Russian? etc.