This is 99% invisible. I'm Roman Mars.

And this is a video episode that we made with Vox.

So if you haven't already, turn on your screen and look at it.

It'll make much more sense that way.

You probably know how this symbol is supposed to make you feel.

And this one. This one too, even if you're not exactly sure 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,

lockbuster 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.

...