If the threat is widespread human and environmental destruction, I wonder if an additional layer of warning does not need to consist of more constrained lethality. "We're going to show you what this stuff is, you should've really paid attention to the warnings."

"It is a place of evil: all who venture into the pit die in agony within a few days," seems like something that would have more cultural weight. And be trivially re-discoverable at any point. People don't go wandering into lava to see what's below. People wouldn't have stripped the Egyptian tombs if the warnings on the wall consistently came true. Perhaps the best warning of danger is danger.

And then, if the threat model is drilling, it seems to me very unlikely that a future mining civilisation would not understand pictures, maps and diagrams illustrating the content. Is an illustration really more culturally ambiguous than language?

Anyway, that's probably the reason that energy line is here. But you'd simply check everything you can measure at the time, conclude superstition and continue anyway.