How do I know if a girl is taken?

Not really, but you can always check for a ring then ask about it. For example, I wear a dinky ring on my ring finger to prevent guys from even asking. Honestly, that's not really saying much, though. You're just going to have to ask.

There are no sure fire ways to tell without asking her. If you know her and her friends, you could ask them. I guess for girls in committed relationships who are loyal to their boyfriends you can pick up some signs. Most won't be flirty. If they're on the phone and say, "I love you." and it sounds more endearing. For big holidays they get excited and have plans. Like Valentine's Day and Christmas. But not all girls in relationships act like that. If you don't want to ask her or ask a friend of hers, just talk to her. Girls like to talk about their boyfriends. Especially if they're really into them.

Nope, the only way you can tell is by asking her.

well if she's got a ring on her left ring finger...
but that doesn't really hold true these days cause a lot of girls wear purity rings.

otherwise, no not really. hopefully, a girl in a relationship won't flirt back with you or whatever, so you shouldn't have to worry about it.

no.

Keep flirting until she either brings up the boyfriend in a positive light, the boyfriend shows up, or she tells you to go way.

All girls are fair game unless proven otherwise.

Usually she will say something when you talk to her, don't bring it up, If she says stupid sh*t like O h I love him he is so wonerful type bullsh*t than go on you way, but If she says something like, oh he such an asshole I think he is cheating on me, or something like that then you may proceed, or if she does have a boyfriend and she tells you(because you never ask because you don't care) than that's god to she might give you some on the side and may even leave her boyfriend if you hit it just right...LOL...

if your friends with her on Facebook/MySpace this could help you out. Check for relationship status/ old wall posts/ pictures...

No way to tell.

But here's a foolproof two-step process to determine if she's interested in you.

1. talk to her.

2. ask her for a date.