Back in the late '50's/early '60's, a drive across Iowa in any direction would subject a person to small, diamond-shaped signs placed by a Des Moines insurance company, all of which featured a big red "X" - which "marked the spot" -and the word "THINK!" These signs were placed where a fatality had occurred due to an auto accident. They were not exactly a skull and crossbones, but the general effect wasn't greatly different.
All this was a bit of creepy to a (then) very young Mr. niteowl77, but what really bothered me was when we would come on a place that had two or more of these signs. I still dimly remember a veritable thicket of them at one particular "T" intersection in western Iowa (on or near Hwy 3, IIRC). As a warning to keep alert, they sure worked wonders on me.
Mr. niteowl77
While laid up after back surgery, I watched a few dash-cam videos on YouTube, It made me a more aware and careful driver but the effect was temporary. Now I make sure I watch a few every month.
When I was younger, I noticed that in Montana there were little crosses dotting the sides of the road all over the place, but especially at odd corners and intersections.
I later learned that they were “death markers” similar to what you described.
Slightly creepy yes, but they are effective, I think.