How will "DANGER!" be written 5,000 years from now? How will it be written in 50,000 years?
Finding an answer to these questions may not seem like a Code Red emergency to most people.
But for a growing cadre of scientists, figuring out how to alert our distant descendants to perilous nuclear waste entombed hundreds of metres (feet) below ground has become a fascinating task.
After more than six decades, high-level nuclear detritus is piling up above ground, and governments are starting to spend billions on underground facilities intended to survive tens of thousands and hopefully hundreds of thousands of years.
That means there is an emerging interest in choosing the right signs and language to warn people of a stockpile that could be deadly, as well as a potential source of military nuclear proliferation -- or even a source of fuel, if future technology can recycle it.