Who are we expecting to have buried things there? I can come up with 6 possibilites, is there another you were thinking of?

Modern humans. In this most likely case it's probably not interesting, maybe some Propaganda Preservation Program from the Cold War.

Recent aliens. I would expect if any aliens were about to jaunt over, notice our space-faring potential and bury a cache for us to discover to mark our readiness to join the Galatic Federation, we would have probably noticed them in other ways by now.

Ancient aliens. Why would visitors before intelligent terrestrial life think it worthwhile to bury stuff just in case we evolved? You've got to have a whole lot of faith in your civilization's stability to think that leaving tags everywhere is a better strategy for continuity than just colonising.

Ancient, non-human but earthbound civilization - Silurians. I could believe that another society might do this, and I think this is who the grandparent is suggesting we aim for - but since we're speculating over geological times the location of the poles is quite variable. Unless we have a fair idea of when the sender lived we don't know where to look, and to find out when they lived we'd need to find the cache... Or you could be saying "hmm, those big extinction events kind of look like the one we're causing now, I wonder where the poles were at those times?"

Some recent but forgotten technological human civilization - Atlantis. Maybe, but like the recent aliens I would expect there would be other signs.

The whole of human history is a lie! - Hiigarans. Fun times.

I don't think it's worth specifically scouting around for something, but maybe if we're buying anyway and it's cheap it'd be worth checking.

Probably better than looking for Dinos on the Moon.

I'm not aware of any effort to do that, but it seems like a moderately worthwhile project (especially if combined with a project to bury stuff in the event that nothing is found).

Only with radar and sonar. And only incidentally.