In Germany, a metal plate embedded in the sidewal have a very special meaning that makes you pay attention to similar plaques elsewhere.
It turns out in some US cities they are also pretty common, and for the reason of protecting the property against adverse possession (squatter’s right) https://untappedcities.com/2020/01/08/the-property-line-markers-in-nyc-sidewalks-offer-crossing-only-by-permission/
