There is a Dutch tradition of leaving curtains open, setting up swags of decorative lace curtains, and arranging ornaments in the windows. Windows are often directly over the street so leaving the curtains open is a privacy loss, but the ornaments do distract your eye.
I was told, by a Dutch friend, that it’s a stroke of Calvinism. This way you can see into the house, and you can see that no-one is up to any naughty businesses. The same reason you have handen boven de tafel (hands above the table), resting your left wrist on the table, while you eat your soup with your right hand. This way it’s very clear to everyone that there’s no hanky-panky going on.
My Turkish friend has a slightly different take on it, he thinks it’s a way of showing off. This way everyone can see what lovely things you have.
I think it’s a sort of social control proclaiming to the world “look our house is clean and we’re so tidy”. While people who close their curtains are somehow shameful and dirty. (No, I’m telling you what I do with my curtains).
In any case I spotted this seasonal decoration in a window in a neighbouring street.