"World Balance" probably have something to do with galaxy.
Above here is the Golden Spiral.
In geometry, a golden spiral is a logarithmic spiral whose growth factor is φ, the golden ratio. That is, a golden spiral gets wider (or further from its origin) by a factor of φ for every quarter turn it makes.
Post-timeskip Sanji's eyebrow have the exact pattern as the Golden Spiral.
It is sometimes stated that spiral galaxies and nautilus shells get wider in the pattern of a golden spiral, and hence are related to both φ and the Fibonacci series. In truth, spiral galaxies and nautilus shells (and many mollusk shells) exhibit logarithmic spiral growth, but at a variety of angles usually distinctly different from that of the golden spiral. This pattern allows the organism to grow without changing shape.
And then this is where Sanji's exoskeleton coming in.
Sanji's eyebrows being a pattern of a Devil Fruit is interesting too.