It is totally okay to be attracted to a stranger, to strike up a conversation, read social cues as to whether she is comfortable in the conversation, learn a thing or two about one another if she's willing to open up, and then politely ask her if she would like to go out some time. Maybe offer your number instead of demanding hers, so she doesn't feel obliged to reciprocate your interest. And respect her decision.
No one is saying two strangers can't talk to one another and become friends—or more! Just don't be a dick, don't be pushy, don't predicate it on her looks or sex appeal, don't make it loud and public, and really do try to learn about one another as equals. Above all, back off if she's uncomfortable.
(That said, I've always thought it's shitty to put someone who's at work on the spot when they're required to be polite to strangers as part of their job and they can't easily retreat.)