Lowercase and Uppercase

Emma was describing one of her classmate's dads to me.
"He has glasses, and kind of a beard and his hair is like a lowercase U."
Me: "Lowercase U?"
Emma: "You know, it kind of goes around."
Me: "What do you mean, like Papa?"
Emma: "Oh no, Papa's hair is like an uppercase U."
Me: "And what about Grandpa?"
Emma: "Oh his is an uppercase U too."