In 2003 Joshua Abbey of the Desert Space Foundation, launched an international competition to design a warning sign to be placed around the site of a future nuclear waste disposal site at Yucca Mountain, Nevada.
The international competition currated 150 finalist designs from an international community of entrants. The Las Vegas exhibition of winning entries drew several thousand visitors and eventually made its way to California and Colorado.
The aim was to generate a system that would effectively warn visitors to the site that the location was extremely hazardous to tresspassors, but here's the catch. The sign must endure for approximately 10,000 years, which is the estimated life span of readiocative waste.
In truth, it is laughable to expect that ANY form of communication could endure for such a period of time, nevertheless, entries were submitted (several of the submissions can be found here http://www.desertspace.org/warning_sign/uwsGallery.html) and a winner was chosen.
"Blue Yuccas" were granted best-of-show, the winning concept coming from UCLA architecture graduate student Ashok Sukumaran. The solution proposed that a genetically altered strain of Yucca be planted around the site, which would grow virally and eventually expand the entire storage location. The concept being that language is rendered useless, so is any sort of semiotic solution, assuming that in 10,0000 years these modes of communication would be rendered useless.
Relying then on an altered species of plant, theoretically found no where else on the planet, this solution would act as genetic warning sign. The blue and aggressive landscape would act as a beacon suggesting that not only was there sometime entirely unique about this location, but that its terrain should not be explored or inhabited.
Essentially, there is no solution. The entire proposition is absurd, assuming that we are intelligent enough to devise a communication system that could transcend such a period of time. But as it is, Ashok Sukumaran was insightful in that he cirumnavigated the language and symbol paradox. I just hope that no one has the misfortune of having to test the system.