I have written before about the all mans right - the right to roam in Norway. What i boils down to is that
in Norway everyone, including foreign tourists has the legal right of access on private property, as long as it is not cultivated land, but it also includes cultivated land in the tiome of year when the ground is frozen or covered by snow. The right to roam also include wild camping, provided you set up camp morethan 150 mters from the nearest inhabited house or cabin, and move camp every 2 days. Yo do not need any permission for this (but keeping a good relationship with landowners is of course adviced).
So how far does this go?
Well, a sign like this is actually illegal to set up. The text says:
Private property
Cloudberry picking prohibited
Property of the owners
The reason it is illegal is that it breaks with the right that the public have to pick berries and nuts for their own consumption
The only way this would be legal, is when the berries have a significant economic advantage for the owner. but then the prohibition shall only be valid for a limited area, for example one specific bog (cloudberries grow on bogs). A landowner cant prohibit picking on his entire land, a whole island, or a largeer area. And the sign must state clearly where picking is not alllowed. But even then you may legally pick berries if you eat them on the spot.
I love traditions :-)