Ask about a boyfriend or not? Daygame approach.

Ask:
+No more wasted time on approach - "You gave compliments to my jeans and we talked about my art major, but I won't give you my number, I have a BF"
+Less ghosting - "I gave you my number, but I thought you just wanted to be friends"
+No bullshit on dates, like - "I had a good time, but not ready to cheat"

Don't ask
-She's maybe ready to cheat, as long as you don't know about her boyfriend and therefore she doesn't feel like a whore

No, don't even entertain the possibility of there being a boyfriend. More than one woman has made up a bf as an early cockblock. Don't offer her an easy out.

Even if there is a guy in the picture, you don't know the status of that relationship. If she is truly in love with the guy, she will let you know.

Even if she claims she is unavailable, you still have important experiential data points on female behavior in seduction.

Today I ran into a woman who 4 years ago tapped my wedding band and said "If you weren't married, I'd ask you out right now" I still remember that, and if I had something in my current relationship go sour, she would be a soft place to land. She's solidly in the 3rd string...but she's an option. The fact that I'm still thinking about that should be reason enough to put your interest out there...