This is called a 'TOP', short for (in Dutch) 'Toeristisch OverstapPunt', something like 'Tourist Transfer Point'. A TOP is a kind of landmark where tourists 'arrive' and can start a marked cycle or hiking route, or any kind of activity. These signs can be found in various regions of the Netherlands. Here in the province of Groningen it's a cone filled with stones, other places have a steal key, or a large stalk for instance.
This particular one is located near the train station in Stadskanaal.