I think it depends on each person, but no matter who you are, when you know, you'll know. You won't need someone else to tell you, and I don't think there's a list of things that every single person can say "Yup, got all those, must be love." All I can say is that, to me, if you have to ask, then you're not in love.
"Voici mon secret. Il est très simple: on ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux."