This one has been in the works a long time -- one of my grad school professors was involved in [unused] design work on a U.S. version years ago, and I remember him talking about the semiotic challenge of crafting a symbol to be interpreted by the post-apocalyptic survivors of civilization, 10,000 years from now. I'm not sure the International Atomic Energy Agency (IAEA) really nailed this one; I'm inclined to agree with Wonkette's assessment...

After many years of research around the world, the International Atomic Energy Agency has revealed the new global warning for ionizing radiation: a terrifying scene of an alien spaceship shooting death rays at a pirate flag and stick figure.

The message of the new logo is clear: Do not trust the space monsters. — Via Wonkette

Or if you prefer straight news to snark, try the IAEA:

"We can´t teach the world about radiation," said Carolyn Mac Kenzie, an IAEA radiation specialist who helped develop the symbol, "but we can warn people about dangerous sources for the price of sticker."

If only we had something for Fox News...