Art: A Moss-Covered Concrete Block.
With three sides and three points, it's the only polygon without a concave form.
Is there a more urban or artificial form than the cinder block? And yet, set in nature, it will be covered with moss, it will accumulate dirt, and a ground animal might even perch on it or live inside.
It isn’t a ruin, but it’s highly unlikely it would be used in a building either. It could be found by the future, be a marker that someone had put it there at some point. For some ritual? To mark a spot? Or had it merely fallen off the back of a truck, which was a device used to cart things before teleportation.
I’ve read about how we could communicate with aliens, or but how do we render intelligible to some unknown future what life was here on earth as we knew it?