I just got back from a weekend in Denmark. It was my granddad's birthday on Sunday and the weather was just beautiful - in Denmark we have a saying that if the sun shines on your birthday it means you've been good during the past year. This isn't really fair if your birthday is in January, like mine!
A lot of Danish houses have a flag pole in their garden. Usually you just have a Vimpel (a long, thin version of the Danish flag), but on special occasions, such as birthdays, the Danish flag (Dannebrog) is raised.
I think it's a lovely tradition but maybe it seems a bit over the top from a non-Dane's perspective?