Maybe I’m just thick. Maybe the billboard makes perfect sense. That’s why I asked a U.S. senator about it. But first:

Planned your summer vacation? It’s a bit late, but you could head to North Dakota, the most beautiful and prosperous state in the union that’s rectangular. There’s lots to see.

Fargo has a marvelous downtown, and if you want to visit the suburban delights, well, you know how the Olive Garden is on the south side of the street where you usually go? In Fargo it’s on the north side. It’s things like that that make travel worthwhile. Shakes you up, takes you out of your comfort zone.

I’d advise against driving to the western part of the state and expecting to find a motel room; housing is so short in the oil patch that the motels have slung three tiers of hammocks in the shower stalls. Submariners complain it’s claustrophobic.

But the drive west on I-94 is almost like meditation. Put a brick on the gas pedal, tie the steering wheel so the car goes straight, and just let your mind wander. Text all you like. Take a nap. There are rumble strips outside of Bismarck, so you’ll be awakened in time.

Some people find the absence of, well, things to be somewhat unnerving. But nothing compares to the immensity of the prairie sky, especially when the clouds mass high and wide. It makes mountains look like old character actors who’ve played the same role their entire career. The clouds on the prairie are like mountains with a talent for improvisation.

The endless prairie reminds you of the nation’s immensity; the unspoiled landscape reminds you how little of this land is occupied by humans; the delightful, kitschy, tourist-trap sprawl of Wall Drug reminds you how you took the wrong highway, because you’re in South Dakota.

Well, there’s not that much difference, really. Both have Badlands on the far end, although North Dakota lacks the solemn civic noggins of Rushmore and the inconceivably large Crazy Horse statue, which, after 60 years of work, has resulted in an absolutely spectacular fingernail. (Honestly, they stand a better chance of letting erosion finish the thing.)

Whichever Dakota you select, there’s another world waiting at the end of the road.

That said, I do not understand the North Dakota tourism billboard. The slogan:

ARRIVE A GUEST

LEAVE A LEGEND

OK. Now. This isn’t like some penny jar at the SuperAmerica — Have a legend? Leave a legend! Need a legend? Take a Legend! It applies to some process that occurs during the vacation.

You arrive as a Guest, which makes sense, unless you were born there, in which case being called “a guest” is like going home and finding your folks rented your room while you were at college. But for most, yes, you’re a guest.

Then somehow, between the act of crossing the border and leaving the state, you become a legend?

Not that you encounter a legend. Not that someone tells you a legend. Not that something happens that you will forever repeat and embellish until the bear cub in the parking lot becomes the Legend of Dad Saving the Family by Punching a Grizzly.

No: you are the legend … to them.

There’s no other way to read that. When you leave, you will be legendary.

Like this, perhaps:

“Yep, been nigh unto 40 years, but folks ’round these parts still talk of the fella who showed up in the Badlands and thought there’d be bike trails. Wore one of them tight costumes where you can see everything. Pitched a fit when there weren’t any trails; called us all a buncha hicks. Well, we may not cotton to city ways when it comes to bicycle roads up and down a mountain, but I do know my cousin took a video of him yellin’ and it got 459,254 hits on YouTube. By the way, none of us talk like this.”

Or: “Say, Harvey, remember the family that came through here, filled up on gas, bought some pop and didn’t use the bathroom ’cause they said they’d just use the next one, when there wasn’t another stop for nigh unto 165 miles?”

“Sure do, Ralph. Folks say they pulled off past Valley City and were never seen again, and at night their spirits walk the land, all bent over with their knees together.”

Seeking clarification, I asked one of the great state of North Dakota’s two U.S. senators, John Hoeven: What does it take to be a legend in the Flickertail domain? It’s already so full of legends!

“The theme for the tourist department is ‘Legendary,’ ” said the senator. “That goes back to Teddy Roosevelt, Custer, the whole Western experience. So I think they’re playing to that. Come and have a great time!” he said. “You’ll love it.”

Custer did. Bet he wished he’d stayed.

Hey, there’s next year’s slogan:

ARRIVE A GUEST

DON’T GET KILLED IN MONTANA