Ever wonder: Why letters are on car locks?

A few days before Christmas, the kids and I were on our way to Idaho Falls. I had to run back inside "for one more thing," and started the car so the kids wouldn't freeze. As I did so, I hit a button and the car beeped at me. I closed the front door, ran in and out with whatever it was that was so important and tried to open my door. LOCKED! and the kids doors...and of course, my keys were in the van! (oh and Bob had the spares since he lost his keys, but we found his "lost" keys in the move, hanging in a pair of pants in the closet!) Anyway, I got Ella's attention and she thought it was a game, "ha ha Mommy can't get in." I told her to unbuckle herself and her face went pale (We have been repeatly telling her unless the engine is off and the keys are out, she better not take her belt off...And now I am outside freezing, trying to get her to do the opposite. The rules we have for our children ) She finally unbuckled and tried to open the door for me, still locked of course.

"Press the U".
"I like the L.
"No, Ella the U."
"L for Ella."
"Ella, please. The U"
"Okay"

I was so happy when she opened the door. I think she was scared when I started to smother her in kisses. What a big girl. Now I won't worry so much next time I get locked out...not that I plan on doing it again soon :) It is way to cold!