If that was all the stones did, it'd be fine. Haunting, but fine. But they're also inscribed with warnings intended for future generations, explaining that if these stones show up, things are about to get a little apocalyptic. They warn us to prepare for bad harvests (check), food prices going up (check), and that things are going to be particularly hellish if you're poor (check).
Some stones are even inscribed with what appear to be wailing laments. A stone in Techlovice reads "We cried -- We cry -- And you will cry." One in Bleckede promises survivors that "When this stone sinks, life will become more colorful again." Our personal favorite is the stone at Decin, which simply reads, "If you see me, weep."