What are subtle signs a man finds you attractive? and if they find you attractive why don’t they approach women?

Do guys look at everyone or is there a certain way they look at someone they find attractive?

Backstory: I was out in the city with a friend and there was this super attractive guy walking with his friend. My friend and I were sitting on a bench and talking and then the two guys walked past us and didn’t look but they walked a couple steps down stared at this building and then walked back. When they walked back the super attractive one made eye contact with me. And as they were walking away they kept turning back and looking. But did he even find me attractive? If so why didn’t he do anything about it?
What are subtle signs a man finds you attractive? and if they find you attractive why don’t they approach women?
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