Well if you want Ultramarine symbols Lodown my omega signs were very simple..
A circle of white, a T across the top, a blue circle in the middle then a tiny line vertically down the middle. I also always tidy up the edges to give it a symmetry(so it's not rough looking)
The crosses were a square with short lines going to centre from each corner, then a white circle in the centre.
If you choose a symbol, try to see other shapes in it to help you break it down for painting. That's how I worked out the Ultra symbol for epic scale.