How do I know if I got a Girls attention?

I was at the gym and I kept checking this girl out, I don't normally keep looking at the same girl, im not gonna lie I enjoy checking out people at the gym it just motivates me that's not just perving on girls but this girl was gorgeous and eventually when I looked I caught her staring or looking at me, how do i know if she's interested at all
How do I know if I got a Girls attention?
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