Unable to answer "For which sport is this guidepost intended?" – Trail Marker – https://osm.org/node/10969317254 via StreetComplete_ee 58.0:

SCEE offers only "its just a simple guidepost", but thouse are just route markers, not guideposts at all? raise issue.
(I popraviti  po Prvicu druge "simple guodeposts" #selfnote)

Attached photo(s):
https://westnordost.de/p/221935.jpg