How do you tell if a girl is single?

What are good ways to find out immediately without directly asking?

Don't say Facebook, because a lot of times people don't post their relationship status.

I'm tired of only finding out after a month, and then she tells me she's in a long-term relationship with some guy somewhere far away in a remote galaxy.
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A lot of people are saying that if you ask a girl out, and she says yes and acts interested in you, then she's single...but I've found that's often NOT the case...


I've even had girls ask me out who weren't single.
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And I don't want to ask directly, because that seems too forward and like I'm moving too fast.
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I've got an idea...if I hint to a girl that I'm single...like say, "I'm almost always free on Friday," or "I haven't been out in a long time"...would she tell me if she's single? Or would that just make me look like a loser?
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Why would girls hide their relationship status anyway? I can see if you're single, not wanting to blurt it out to the whole world. But if you have a boyfriend, why hide it? Girls seem to almost avoid talking about their boyfriend around other guys...
How do you tell if a girl is single?
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