Some things, like the passage of the sun in the sky, should be universal. Literally every civilization on Earth is familiar with the concept of a day. Death is a universal concept too.
Of course there is no helping if the future people are especially dismissive of your warnings, but they should suffer from debilitating radiation sickness before they get too far away, so at least the leak would be somewhat contained.
Interesting story idea for a post-apocalyptic agrarian society where some guy wipes out his rival's towns by lightly burying preapocalyptic nuclear waste in the town square to kill off the inhabitants while preaching about curses and gods smiting the inhabitants for their sins.
Yeah time was meant more as just an illustration of how careful we have to be with and pictographic warnings because of how little we can take for granted about the people we are trying to warn.
Of course there is no helping if the future people are especially dismissive of your warnings, but they should suffer from debilitating radiation sickness before they get too far away, so at least the leak would be somewhat contained.
Interesting story idea for a post-apocalyptic agrarian society where some guy wipes out his rival's towns by lightly burying preapocalyptic nuclear waste in the town square to kill off the inhabitants while preaching about curses and gods smiting the inhabitants for their sins.