Long-Term Nuclear Waste Warning Messages are intended to keep nuclear waste storage facilities inviolate, undisturbed and safe for 10,000 years- the approximate time period that spent nuclear fuel remains dangerous. This is longer than any human-made record or structure has survived, and easily longer than any language has remained understandable by the common person. Therefore, they are constructed with the assumption they will need to be effective after the fall of current human civilization.
Several of the suggestions have involved "spike fields" or massive blocks of concrete or granite, rendering an area inhospitable, forbidding, and worthless for agriculture or human habitation. Teams from Sandia labs also came up with several "messages" that they wanted the imagery to convey, two of which are condensed into these patches. It's pretty fascinating stuff, and you should look into it. Here's the Wikipedia page to get you started.
Of course, humans being humans and idiots, these warning messages may perversely encourage exploration of these dangerous sites. Pharaoh's curse and all that.
These patches are 3.5" across, hook fastener backed, and available in two versions as seen above. The "both" option comes with one of each. Also available as stickers here, or as a combination bundle with the patch and sticker together here.
Art by Jade @JadedPencil