These signs can be found all over Switzerland. They point to walking trails. Often they have a destination on them as well as how long it will take the average walker to reach that destination.
One of my favorite activities to do is go to the train station, catch a random train (all public transportation is included in the pass we purchase) get off at a cool looking village, find a wanderweg sign, and go on an adventure hike.
We found this one in Bern that took us on a trail along the river.