Circles seem to symbolize many things in the night circus. A circle is considered the most simple shape. In this picture, the circles are unique and decorative, much like the circus. These circles symbolize how nothing about the circus is simple, instead everything is intricate and complicated.
Circus backdrop inspiration. Source: http://us.123rf.com/400wm/400/400/tintin75/tintin751205/tintin75120500002/13662833-a-retro-circus-poster-for-your-advertising.jpg ; Some sort of circus texture/card thing, which really displays the old retro vibe about the circus, very well. This was the kind of vibe I wanted in my animation.