In context of overlay "Things" – Boundary Stone – https://osm.org/node/7926171788 via StreetComplete 62.2:

3-Märker?

Attached photo(s):
https://streetcomplete.app/p/327618.jpg
https://streetcomplete.app/p/327619.jpg
https://streetcomplete.app/p/327620.jpg
https://streetcomplete.app/p/327621.jpg
https://streetcomplete.app/p/327622.jpg