And this one.

This one too, even if you're not sure exactly what it means.

But what about this?

This symbol — The Jolly Roger — was once one of the most feared symbols in the world.

It represented death, pirates, and poison.

But today,

it's associated more with treasure, blockbuster movies, or Halloween than actual danger.

We are surrounded by icons that warn us: what to stay away from, what not to do, what to

be afraid of.

But how do you design a symbol in a way that will last across generations and languages?

It turns out that is an incredibly hard thing to do.

Back in the early 20th century, there was an urgent need for a new kind of warning symbol.

At the time, there was no universal standard for communicating the presence of dangerous

biological materials.

Laboratories at the US Army used an inverted blue triangle.

Those at the Navy used a pink rectangle.

The Universal Postal Convention used a white staff-and-snake on a violet background.

There was no consistency in the visual language used to communicate risk.

That was dangerous, and could lead to accidental infections.

So in 1966, a group of engineers and designers at Dow Chemical set out to create the best

possible icon for biohazardous materials.

They laid out six design criteria.

First, it needed to be visually striking, so that it would draw immediate attention.

That ruled out simple shapes like those from the Navy and Army.

It also had to be unique and unambiguous, in order not to be confused with symbols used

for other purposes.

That ruled out the snake-and-staff, which has multiple versions and has a pretty vague

meaning as a general symbol for medicine.

On top of that, it had to be quickly recognizable and easily recalled.

Had to be easy to stencil.

And rotationally symmetrical, in order to appear identical from all angles.

And lastly, it had to be acceptable to groups of all backgrounds.

So the Dow Chemical team designed an experiment.

Charles Baldwin, an environmental health engineer behind the experiment, said that the team

“wanted something that was memorable but meaningless … so we could educate people

as to what it means."

They showed a set of 24 symbols to 300 people from 25 American cities.

There were 6 newly-designed biohazard markers, and 18 common symbols — things like Mr.

Peanut, the Texaco star, the Shell Oil symbol, the Red Cross, and a swastika.

Participants were asked to guess the meaning of each one, which was used to assign each

one a “meaningfulness score.”

A week later, the same participants were shown those original 24 symbols, plus 36 more.

They were asked to identify which symbols they remembered seeing in the previous round

of the study.

Among the six competing biohazard designs, this one stood out.

It scored the highest in memorability, but the lowest in meaningfulness.

So it was unforgettable, but also a totally blank slate for designers who wanted to give

it meaning.

And with that, it became a national standard.

It's easy to overlook how much visual communication work these symbols are doing.

They're simple — you only need a straightedge and a compass to recreate them.

And unlike most other hazard symbols, they don't reference an existing physical object

or idea.

But they've remained iconic for decades, helping people recognize serious dangers that

may remain a threat for thousands of years to come.

And that raises the question: could the meaning of those symbols stand the test of time?

Few people have pondered that question quite like Gregory Benford.

He's a physicist and science fiction author.

In the 1990s, he was invited to work on the Waste Isolation Pilot Project, or WIPP.

The WIPP is a massive storage site for radioactive waste in the southeastern plains of New Mexico,

organized by the US Department of Energy.

Benford was brought in to help calculate the probability that someone or something would

intrude on the site for as long as it remains dangerous — approximately the next 10,000

years.

“Well, name anything that has persisted for 10,000 years.

Any institution.

There isn't any.

The record is probably something like the Catholic Church or the core of the Jewish

religion, which tells us something about what really lasts.”

The meaning of a symbol can change over time.

Like the Jolly Roger, which wouldn't work for the radioactive threat at the WIPP.

"If you're approaching the WIPP facility and you see a skull and crossbones you might think,

'Hey this is where the pirates buried their treasure.'”

So how do you indicate a long lasting danger across any language?

Since the 1970s, engineers, anthropologists, physicists, and behavioral scientists have

proposed different solutions to that problem.

One strategy was to add context to the symbol.

By illustrating cause and effect in a three-part cartoon like this, designers could communicate

the idea even if the symbol lost its meaning.

But this kind of visual communication still made a lot of assumptions about the user:

that they would read left to right, that they would understand causality between frames

— and, of course, that the drawing itself would last millennia of wear and tear.

So other designers started to focus on creating a warning without inscribed communication,

by altering the shape of the location itself.

And that yielded designs like this.

Spike fields, forbidding blocks, giant pyramids: these designs capitalized on natural instincts

of fear and discomfort to keep people away.

But even then, they weren't foolproof.

Designers couldn't be sure whether they would be perceived as terrifying or fascinating.

“Conflict between these two urges: you want people to notice it but you don't want people

to go there.

Those are always going to fight each other.”

So without symbols, without basic illustrations, or physical structures, how can you effectively

communicate a warning?

That's where the more philosophical design solutions come in.

In 1984, the German Journal of Semiotics published a series of solutions from various scholars.

Linguist Thomas Sebeok proposed creating an atomic priesthood, where an exclusive political

group would use its own rituals and myths to preserve information about the radioactive

areas.

And philosophers François Bastide and Paolo Fabbri proposed to genetically engineer bioluminescent

cats that would glow in the presence of radioactivity.

By creating songs and traditions about the danger of glowing cats, the warning could

last as long as the oldest relics of civilization we have: culture.

There's no definitive solution for warning people far into the future.

But designing clear, inclusive symbols will continue to be a fundamental part of how we

keep people safe.

We will change, and so will the ways we communicate visually.

Our warning symbols will have to change along with us.