Yarn installations, or yarn bombs are not permanent, and unlike graffiti, can be removed if necessary. Nonetheless, the practice is still technically illegal, though it is not often prosecuted vigorously. Yarn bombing is about reclaiming or personalizing sterile and cold urban environments, or altering on object in an adorably unexpected way.
I have a handful of these random little circles in my stash, so I started out with a green and blue one, and just "free-styled" it from there.
I started small. And decided that this no parking sign could use a little flair. It stayed up for at least 3 days, though I haven't checked on it recently.