Zone 1,2,3: In 1920 elections were held whether the area of Schleswig should go back to Denmark. Zone 1 was the most northern zone. Zone 3 was the most southern zone. Zone 1 voted first, and they voted Danish. Zone 2 voted German and so elections were cancelled in zone 3. See also the map here.
Bismarck: Chancellor of Prussia 1862-1890. They put a statue of him on the hill Aschberg near Ascheffel. read more about him here.
The Border Society: Is the main organization in Denmark with local chapters all over the country that mobilizes support for the Danish minority. Because it is no longer normal to have huge flag parades, they instead have to participate in the ones in Southern Schleswig. Their website is here.
The Schleswig League: Is a minor, but more radical organization in Denmark that also mobilizes support for the Danish minority. Their original goal was to get the Southern Schleswig reunited with Denmark. Although they nowadays say that it is "unrealistic" to achieve that goal, their website still focuses a lot on it. The League does not receive government support fopr its support projects in Southern Schleswig. Instead they collect money from private individuals. Their website is here.