How do you tell if others find you attractive?

I'm not drop dead gorgeous or anywhere near that, but people can usually tell from an outside perspective if someone likes you or finds you attractive (since everyone has different tastes/standards). Or even just for friendships? How can you tell? Or how do you tell if a stranger is checking you out or if your being looked at because your ugly? I just feel like socializing would be easier, but I don't know if this is a learned skill or always unknown.