Color Changing Cats Ocean Waste Crypts No Man's Lands A Unique Radiation Symbol 
Answer: Color Changing Cats
In 1981, a task force known as the Human Interference Task Force was created through a joint effort between the U.S. Department of Energy and the Bechtel Corp. (the largest construction and civil engineering company in the United States). The goal of this task force, comprised of engineers, anthropologists, nuclear physicists, behavioral scientists, and others was to propose plans to protect future human civilizations from the hazards of radioactive waste.
How do you go about protecting humans, perhaps 10,000 years in the future, who most likely don’t speak your language and may no longer have the technology to detect and understand radiation? The task force determined that any method they proposed would have to meet basic guidelines: it would clearly need to be a message, it would need to communicate that dangerous material is nearby, and it would need to communicate something about the type of dangerous material.
Some of the proposals seemed practical. One of the proposals hinged on the installation of stone markers carved with warnings about the site, written in the most important global languages. The signs would include not only warnings, but instructions to install new signs further away from the current signs with translations into new languages (while leaving the older ones intact). Thus not only would the site be clearly marked, but the stone markers themselves could serve as a sort of Rosetta Stone that would allow for the translation of old languages. Not a bad or outlandish proposal, really.
Some of the proposals, however, were a bit outlandish, including the one that is the topic of today’s trivia: color changing cats. This particular proposal hinged on the idea of genetically engineering cats such that they would change significantly in color in the presence of radiation and weaving the idea of color changing cats indicating invisible danger (radiation exposure) into fairy tales, myths, and popular stories. The argument was that even if people lost technical knowledge over time, these fairy tales and myths in turn could be transmitted through poetry, music, and paintings.
Although the radioactive-cat project never came to fruition, the meeting of the Human Interference Task Force was still a landmark event as it was the first instance of nuclear semiotics–the research and deployment of symbol-based nuclear warnings.