I tend not to. Yes some may have insanely jealous boyfriends, but it's harder to tell in the absence of visual clues. Typical muslim garb is a signal which does tend to stand out in some circles, and that's one of the things I infer.

No, I don't think every time I look at a woman in a hijab she will be killed, but it does come in to the back of my mind more often than it does when seeing other women in local shops/stores/malls.

Is it prejudicial, as in pre-judging? Yes. People wearing certain types of garb send out signals intended to portray specific meaning. Sometimes extra meanings they didn't intend are also inferred.