Y'know how the standard red-and-blue Interstate shield comes in two different sizes? Narrow for 1- to 2-digit route numbers, and wide for 3 digits?
Well, I've noticed that on many signs in Houston, I-10 appears in a wide shield, and I-610 appears in a narrow shield. Here's a photo that shows examples of both, side by side on the same sign!
Now, I can understand putting '610' in a narrow shield, because that '1' in there doesn't take up much room... but why put '10' in a wide shield? Bizarre.