These small stainless steel
knuckles in the photo on the right are to be found all over America on the edges of concrete.
Will anthropologists of the future know what to make of these?
I'll make a record for them. America has always been a society where teenagers are rebellious against their parents and society. Teenagers rebel in many ways and are virtually uncontrollable by adults.
In the late 1970s a flat board with four wheels on two flexible axles came into common use by teenagers. It is called a skateboard.
Teenagers were able to ride their skateboards on most flat smooth surfaces. Since the range of surfaces for riding included the edges of all concrete withing four feet of the ground, the adults, via their local governments, began putting metal clips on the concrete to keep skateboarders from using them to skate on. A sign saying "no skateboarding" or "respect public property" would have been incomprehensible to teenagers of the period.