If not mistaken, today they are used in a few ways (as referred to in Wikipedia) one is to memorialize a spot -- you see many "crosses" nowadays on the side of the road, consider it similar.
The other,
more common is their are people who literally "treasure hunt" items -- the sport is global and is referred to as Geocaching
https://en.wikipedia.org/wiki/Geocaching
a friend of mine use to do geocaching as a hobby and (among others) there are at least 2 locations on Stonedam and one that I know of (from him) on Bear
.