Hong Kong Flag by Roy Zuo

Ratio
Red:White:Blue = 1:1:1

Symbolism
Reusing the colours and the layering (i.e. blue overlaid by white overlaid by red) of the Union Jack. Circles represent the diversity of the Hongkonger nation and culture. Concentricity symbolises Hongkongers' unity.

Both concentric circles and a square shape are unique features even among all flags and coats of arms in the world, so this design would stand out distinctively and not be easily mistaken for another symbol.