Admittedly, I haven't read the article, but the tone of the message suggests that it's not meant for future generations of our civilization, but for future generations of whatever cultures come after our civilization is gone.

There's a pretty remarkable old English poem that survived from Dark Ages Britain, in which the author marvels at the ruins of Roman Britain, wondering what giants must have once inhabited the land in order to build such things. From the sounds of it, these markers are targeted towards people like that, not our own immediate descendents who will already know it's a nuclear waste site.