I was once told, probably sometime during my wife's pregnancy, that the day your child smiles at you for the first time will be magical and amazing and will melt your heart and make you realize you have a little person, etc., etc.
And when my daughter smiled at us for the first time, it was all that. It really did send me to another place. But I knew she was "my daughter" when she started making what my wife and I call "The Scrunchy Face."
It is exactly what it sounds like - my daughter will, in moments of happiness (laughing or babbling), scrunch up her face in a "super smile" that is both insanely cute and wildly entertaining. Her eyes crinkle and her dimples will pop and she will smile her biggest, almost toothless grin.
And the best part about it is that, when she does it, I do it right back to her and we look alike.
Now it may seem strange that it would take something like this to make me feel like she is my daughter, especially since a lot of people have said she looks like me. It's not her looks, though, that I am talking about. It's the fact that when she does it, I do it back to her - and we both laugh.
So, more than my "looks" (God help her), maybe she has my sense of humor. And that's something unique to me and her.
And that's how I know she's my girl.