Is continuous knuckle cracking a subcontious sign when a guy likes a girl?

That's an interesting one. My bloke used to rub his thumb against the sides of his index fingers unconciously when we first met. I'd say it might be a tell or a nervous habit of sorts. I wouldn't say it's a sure fire way to know he's attracted to her, but more like a sign that he's thinking about it- if he's doing it unconciously.