So essentially the face is like the epicenter of communication so when you’re sitting down having a conversation with somebody you’re not looking at their arms or leg most of the time. Most of the time you’re paying direct attention to the face and for the most part there’s a lot of different signs of attraction in the face.
One of the most useful things without a doubt is going to be smiles, so smiles and laughter. You tend to see that when someone’s attracted to somebody you tend to see a significant amount of smiles. Like when you’re on a date and no one smiles once, not a good date.