Ooh, a highway! My favorite has to be when the letter is mistaken for a directional suffix, e.g. "State Highway North". I even saw the letter O mistaken for a direction suffix in the TIGER import (what direction could that mean?)

Sometimes they're mistakenly referred to as county roads, too (e.g. "N Cl N Highway"), which I bet hearkens back to the Takeover Program. Dunno for sure, though. I wish I could know the rationale behind some of these names.