The Wikipedia article seems to only cover the conceptual idea, and I remembered that there has been a concrete implementation, too. After a short google, I found at least this Atlantic article:
In New Mexico, not too far from where the original Trinity test was held, is the Waste Isolation Pilot Plant. Almost 2 million cubic feet of radioactive waste is buried half a mile deep in the 250-million year old salt deposit. The plant will continue to receive nuclear sludge from around the country until 2070, when it will be sealed up for good. The government half-heartedly anticipated the dangers to future humans and settled on surrounding the plant with obelisks containing messages in Spanish, Navajo, Chinese, Latin, Hebrew, and English.
The Wikipedia article seems to only cover the conceptual idea, and I remembered that there has been a concrete implementation, too. After a short google, I found at least this Atlantic article: