When moving around Indonesia, I have noticed that some houses have this sign sometimes:
What does it mean? Is it just a decoration or does it have some meaning?
The best I can figure this there is a party of some sort going on at the house that arrow is pointing to. The Janur Kuning is traditional ornaments, not to be confused with the Movie under the same name, that appear to designate the house where a celebration or a ceremony takes place.
The particular image that you posted is also visible on Wikipedia's French Page for Party. Most commonly I found this type of symbol to be referring to or used in conjunction with a wedding.
It is put up in front of the bride's house before the wedding.
UPDATE: As I was asked for reference... I am currently staying in Indonesia and showed the picture to my local friends. They told me about the meaning. I also asked whether it's just common here in Java (because in indonesia every region has it's own traditions), and they replied it is common in all of indonesia.