This, right here, screams the whole premise is nonsense. You don't label something very dangerous if you want to prevent primitive people from accessing it.
This project is not really about storing radioactive materials, but about the question "how do we spook stranger future people 10000 years from now so they won't dig here". Utter pseudo problem.
A high-level radioactive material ("waste" in the language of the current primitive nuclear technology prism) that you don't want to use anymore does not need "proper signage". Proper signage is needed only if you plan for people to access it.
If you really care that nobody can access it anymore, you dump it in inaccessible way, e.g. at big depth of Earth's crust at a not exactly known location, and then completely collapse the access holes. Most likely nobody will ever find it and get there.
If you do not really care about that (present governments), just dump it in a water pool near the power plant, or store it in a protected, easily accessible underground dry deposit. Much of "nuclear waste" is still a precious unburned nuclear fuel that people will want to use, after all.