You have misunderstood. Once some individual humans get sick or die. Even very primitive human cultures in the vicinity of nuclear sites would very quickly not

You have misunderstood. Once some individual humans get sick or die. Even very primitive human cultures in the vicinity of nuclear sites would very quickly notice a pattern. Any symbol that was used consistently near nuclear sites would be come to be associated with danger. In a very primitive cultures with no knowledge of science, visiting the sites with these symbols would end up becoming some sort of religious taboo. The argument isn't the the meanings of symbols can't change. But rather that humans are smart enough to notice patterns and communicate them with others.