Take a skull-and-crossbones. It might be taken to mean danger or poison. Or it might be taken to mean pirates or treasure. And if the future explorers did connect it with danger or poison, why wouldn't they also just think it was maybe a superstition meant to keep outsiders from getting "the good stuff," like the curses that were sealed into ancient Egyptian tombs?

What about when the time of Mammals is done, and the next inhabitant has a chitinous exoskeleton? I'm not sure they'd recognize bones as a sign of this place being dangerous.

Yeah, Carl Sagan was like "skull and crossbones"

But of course everyone else wanted to over-engineer it, so you get proposed solutions like encoding messages in the DNA of plants, and color-changing cats with an accompanying viral song that no one's ever heard of twelve years later... 🤦‍♀️

Like, guys, if people today can't even figure out what it means, then it's not a universal and enduring message.

And then some of the suggestions would only serve to make it a glaringly obvious archaeological dig site.

Skull and crossbones is about as universal as you can get. Maybe some atomic diagrams and radiation symbols, and written warnings in as many languages as possible, just in case people still understand them. And a giant slab that someone could only drill through deliberately, requiring heavy equipment.

I can't believe these were supposedly some of the smartest people in the world, and yet they made the mistakes of assuming that future civilizations would be hyperintelligent and thoroughly inquisitive, while also not understanding any symbols from our era and being likely to avoid areas designed to seem ominous. As if egyptologists today respect the warnings on ancient tombs.

And yet they overlooked the skull and crossbones because it seemed too obvious. The whole point is that it's supposed to be obvious!!!

The symbol you need is bones. Bones are always associated with death and decay because after death, bones are the thing that’s left.

I think the only way to get it taken seriously is to include depictions of the site and depictions of what radiation sickness looks like.

Make like a 100 page comic that starts with someone opening a cask and removing a fuel element, then dying days later, the element leaving contamination, which kills someone else months later, causes birth defects, etc until it's returned.

You're not going to scare a society into never investigating something, but you might be able to convince them to put it back and bury it again after they realize the predictions are accurate.

There was a conference about this and Carl Sagan was invited, but couldn't come. He sent a letter suggesting to do just that - skull and bones symbol.