You know what they are, even if you don't know you know. I don't know if it is the correct termonology but it is the word I am going to use for it.
My kids and I were watching Goonies and my oldest son asked a question about the kids with the asthma inhaler. He didn't know his name, but he knew his tagline. It is a great tool to identify each of your characters, make them memorable, and in this case give the hero a weakness. Steven Spielberg also used things like, data- the smart kid with the all the gadgets, or chunk for the chubby kid. It is brilliant when you have so many characerters.
In the book I am currently reading, Crashed by Robin Wasserman, she keeps referring to a minor character as 'just call me Ben'. It is perfect because he is important but hardly there, so it helps you remember him.
I took a class and we were told to give each of our characters some kind of quirk or physical defect. I love this tool for writing. It gives an interesting tidbit along with a identifiable characteristic. I recommend it to all writers, and challenge readers to find them when they are reading, or watching movies.