Do you not look at all women because they might have insanely jealous boyfriends who will then kill them for that too, hey it's technically possible right, so you should err on the side of caution?
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.
http://en.wikipedia.org/wiki/Honor_killing_in_the_United_Sta...
Women who wear head scarves while being perfectly happy to make eye contact are statistically higher than both, by a huge margin.