these signs / markers seem quite recent and I wanted to deepen the reason why they are on Polish soil, recalling that the Council of Europe had launched "The Cultural Routes program" (in fact) in Europe.
The launch was "inaugurated" in 1987, with the certification (probably backwards) of the "
Camino de Santiago".
Subsequently, to further consolidate this proposal, an enlarged Partial Agreement (EPA) on Cultural Routes was formalized in 2010, to give the guidelines and strategy of the program and better determine the criteria for obtaining certification of "Cultural Route of the Council of Europe".
Then other itineraries have been added over the years:
The Hansa 1991,
The Routes of the Vikings 1993,
The Via Francigena 1994,
The Heritage Routes Al-Andalus 1994,
The European ways of Mozart 2002,
The Phoenicians' Route 2003,
and also
the European Itinerary of cemeteries 2010 (new for me )
and many others ....
There are criteria for a cultural itinerary to be certified, including: referring to a theme representative of European values and shared by at least three countries part of the Council of Europe and members of the EPA. Poland joined as a member in 2017.
I assume that the above "traces" are around this year