"If they’re into you, you’ll know."

There was a meme going around a while ago that said something along the lines of:

"If they're into you, you'll know. If you're confused or feel like they're sending mixed signals, they're not that into you."

Do you all agree or disagree with that? It rings true to me, and I certainly make it abundantly clear when I'm seriously interested in someone. But are there any of you who play it cool even when you really do like someone?