We'd be careful but if there was a "I have no mouth and I cannot scream" sort of horror lurking beneath we'd suffer the consequences no matter the warning.
One of the afterthoughts in that document even suggests that the most likely reason people would leave the place alone would be when people die of radiation sickness after breaking into it anyway. It just takes one group of really determined people with a decent amount of time on their hands to destroy the markers and everything else. If asked me how long I would guess until that happens, I'd say less than 100 years. If not then, how about if it's so scary that a religion arises that considers the area to be the home of an Adversary of some kind and destroys it in a holy war?
Yesterday an article on a "paint factory" claimed it to be 45,000 years old, FWIW.
If the message is simply: "There is something dangerous here", we'd probably ignore it. If the message is "There is waste from the fission of uranium buried here. It consists primarily of the isotopes I-129, Cs-135, ... Here is how the waste is stored and laid out ...", we'd be much more inclined to listen. That's what the original document proposes as well, that there should be a hierarchy of messages from "There's something dangerous buried here" to detailed descriptions of the nature and composition of the waste.
There is a particularly good episode of 99% invisible (podcast) that talks about some of the challenges involved.[1]
[1] http://99percentinvisible.org/episode/ten-thousand-years/
> Of course we'd dig around. That's our human nature. We're curious.
If the WIPP messaging does its job, you will have at a minimum been warned that the contents of the vault are dangerous and will make you sick. If you've got the stuff needed to run a complex digging operation, you'll hopefully make something of the Level III and Level IV warnings. And, yeah, if you read all that stuff and decide to dig anyhow, good luck to you. At least it won't be a total mystery if your workers start to get sick.
Perverse and contrary monkeys that we are, there is no better way of ensuring that some future person will dig it up than to have all sorts of signs telling them not to do that.