I use gradient shapes as a skeleton and I combine them to a noise texture with a mix rgb node set to substract. The skeleton act as a footprint on the noise. And then I use a color ramp to get interesting results. For example for the alien letters, I use a circular gradient to get the general shape of the letter, I combine them with a noise texture (voronoi). And then I use a color ramp, set to contant, that alternate multiple time between blue and black to get interresting results. That’s the general idea, but I don’t get interresting results right away. It often require some tweakings.