Any civilization advanced enough to dig deep enough will quickly understand that the material is dangerous.
Well look, there's only really one civilisation we can look at to see if this is true, and that's our current civilisation. It turns out, though, that this civilisation learned to dig through clay and boulders to any depth a few centuries before it understood what radioactive nuclei do to the human body. It's fair to say a new civilisation would probably learn quickly why all of the people mining near the glowing rocks were dying in pain, but progress in that area would probably be measurable in agonising deaths, which is presumably what people are happy to spend money on these signs to avoid.
Having the same sample of one civilization, it has never been particularly deterred by threats of evil and curses on those who enter. If anything, that only increases its curiosity.
Over ten thousand years, erosion or earthquakes can expose the entrance, contaminating the site. People could dig a well or prospect for minerals. The suggestion of underground activity could suggest to them that it is a good place to mine, or even that there's a tomb or other interesting artifacts
Eh, that is is putting way more importance on coincidences than is actually warranted. But lets not loose sight of the general idea.
We need to deal with this waste, on that we are all agreed, we have limited resources to do so.
This means that we need to prioritize the actual waste containment rather than building some weird scarecrow to scare people away who may not even use the same concepts let alone language as we do.
For me, it shows a compassion for the people of the future, which is inspiring in a way. Similar to the Voyager golden records, which are unlikely to ever be found by anyone, it is partially an exercise in understanding ourselves.
I'd rather they showed compassion by not wasting resources and built the proper waste disposal sites so that we can increase nuclear power use and shutdown coal/oil/gas.
Global warming is a way bigger threat than at worst a few localized hazards.
Any money diverted from waste disposal to this idea is wasted.