Is it always a bad sign when a girl crosses her arms?

I've read from numerous sources that when you're flirting with or dating someone and theory cross their arms and they are not cold, it usually means something is wrong. As in she doesn't like you or is bored or upset with you at worst.

How true is this?
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I should have mentioned that this happened on a date. I'm hoping she's not completely disinterested. We seemed to have a good time. It happened in the middle of our conversation at the dinner table. Toward the end of the date she wasn't like that and sounded more cheerful.
Is it always a bad sign when a girl crosses her arms?
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