I actually just had an experience with this situation. I'm going to school over the summer session(right now), and the days my school has orientation(few times a week

) there are a lot of HB's with their parents. So, I saw a hot blond walking with her mom and dad, and I walked up to her and used the David D line,
BTW, I didn't get any eye contact or signals for me to approach, she was walking away from me. I didn't want to let this opportunity slip away because of the fear of approaching with her parents present.
Me: "Excuse me, Can I ask you a quick question?"
HB: "Yea"
Me: "Are you single?"
HB: "No, sorry"
Me: "Well, ok, have a good day"(I don't want to deal with chicks with borefriends).
Her parents: STARING at me wondering what balls this kid must have to come approach their daughter with them right next to her

.
Me:
walking away with a big smirk on my face
Yes, I did get rejected, but my fear(father chasing after me) didn't come true and everything turned out fine. I think it all depends on how you ask her. If you go up to her and say something like, "Hey babe, you do!" then I believe you will have an angry 50 year old father chasing after you, but if you do it in a non-sexual way then I think the parents or parent wouldn't mind. In fact, they probably think you have guts to do something like that because how often do you see anyone do that.