Yes, we can. It's not always apparent because some of you guys like to not show it for whatever reason. I usually can tell when a guy likes me. If I don't do anything about it's because I'm not sure about him yet or I just don't have any romantic feelings for him. On a rare occasion I miss it, it's because I only see him as a friend and nothing more.
Not just attraction but all feelings. When two women start talking to each other we play a little game, every time, where we try and detect how the other is feeling (if they're Okay or Need to Talk) while at the same time trying to avoid detection by the other (who we don't want to burden with our problems) - the game of cat-and-mouse can go on for hours before one finally unlocks the other's guard and she confesses, oh god! I'm in hell! I can't do this anymore!
In all likelyhood if you're crushing on a girl she knows, and she's strategising.
Not all women can detect and pickup signals from people. I can pick up on it a mile away as I am very intuitive. I also will know if it's innocent or sexual. It may end up be deep in the connection to the point I will know if your into things I don't agree with. I can feel their presence and sense their true intentions behind the mask. Too be honest it's not comfortable to always feel something you can't control. But it depends on her and how well she is deeply attuned to her emotions and the things beyond your natural senses. Women are naturally like this, but not many mature or grow on that level to the point their naive and miss subtle cues. Or they don't practice observing things, so they have to ask somebody who is more experienced in that area. And some men can do it too but not all. I always say 'Silence says a whole lot of things/everything'.
i can, and im not sure about all the introverts on this, but i usually judge a person very quickly and judge them right, i mostly have vibes coming from people. but i observer them very much before judging them