Driving through South Dakota, eventually you notice the signs. It's not immediately clear what they mean, but they're all over the place. “X Marks The Spot,” they say. “Think! Drive Safely.” On the other side, the same design, but instead of “Think!” it's “Why Die?”
Eventually, you figure it out, or you Google it and end up on this page: they are officially called “fatality markers,” and the state of South Dakota places one at the site of every auto accident fatality.
The program started in 1979, so there are a lot of signs. They are placed off the road, usually near the right-of-way line, often on the cattle fence. They aren't put up if the victim's family objects. If they come down, by accident or construction or whatever, they are not replaced unless the victim's family asks.
The placement means they're not right up in your face. You're driving along, and you see one off to the side, and hey—someone died here doing exactly what I'm doing right now.
Sure, you could argue to yourself, maybe they weren't. Maybe they were drunk or doing something else stupid. But not all of them were; some were just on their way to Mount Rushmore, or the Badlands, or the grocery store. The road from Spearfish Canyon to Deadwood has quite a few signs. And not one of them was part of the plan.