Do you have a mustache? If you said yes, chances are that you are a Dad. If not, you're probably a pedophile.
But seriously now, chances are that your Dad had a mustache at some point. It's unwritten law that he have one. He'll make a point about having it groomed and not remember what his upper lip looks like without it. It proves his manliness and his masculine hygiene. College guys dedicate all of March trying to replicate one. Girls are reminded of their father figure upon seeing it on a guy (Warning: this can be both good and bad).
This simple act of growing one symbolizes being a father. Don't believe me? This comic says it all: