Not only do the U and N have similar shapes but all 4 letters have a rounded shape. 3 Have a vertical line

Thus I have taken the circle and line to it's absolute minimum to form the 4 letters.

This design uses the negative space to create the 4 letters.

There is a rhythm created like a wave through the design - top of D circle / bottom of U /top of N / bottom of C.

Neutral colours are greys with a little yellow added to soften it from black and white but maintain an elegance.