RAY: The inspiration for this puzzler was sent in a decade or two ago by a fellow named Eric Orr. Actually, it was just a few months ago. And, of course, I had to completely scrap what he sent in.

TOM: He sent you the kernel of the idea.

RAY: Exactly. Here it is:

I remember a day some years ago when I got into a scrape with the law. Okay, I got stopped for speeding. It was an unmarked state police car that pulled me over. As he drove off after handing me my license and speeding ticket, I looked his car over, trying to find something that would make this unmarked car easier to spot in a crowd of cars the next time.

Well, the one thing I did notice - there were no other features really - was that this car had something called "half moon hubcaps." They're the kinds that cover only that part of the wheel where the lug nuts are located. They don't cover the entire wheel like traditional hubcaps.

Over the next few weeks, I began to look at lots of police cars, both marked and perhaps even unmarked. Most of them had these very same hubcaps, and not the full wheel hubcaps that most civilian cars had.

The question is why do you see these kinds of hubcaps on police cars? By the way, you do see them on some civilian cars. You see them on hot rods, for example--and it may be that they're on hot rods and police vehicles for the same reason.