People are being injured or killed each year because they don’t recognize or understand the existing trefoil symbol.
So in 2001 the International Atomic Energy Agency (IAEA) decided to investigate possible new signs and symbols as a supplement to the existing symbol. They took the best of the possible new symbols to children internationally as some of their test subjects and interviewed them on which symbols or colors they recognized and what it meant to them.
For instance, people recognized the color red as meaning ‘warning’ or ‘danger’. Quite a few kids thought the existing trefoil symbol represented an airplane’s propeller.
The intended message of the symbol is “You are in danger, Stop! And run away”. This new sign will likely be placed in an area to warn you if you’ve gained low level access to the lead shielding of a radioactive device and are just one step away from being irradiated should you dismantle the device. The existing trefoil symbol will probably remain as a high level indicator of radiation.