They don’t seem to be in fashion so much now, but I like a classic old school shield pattern painted on a flat shield. Here’s some I did last year. Usually I make them up as I go along. I paint a base colour on the shield, then I think of something to put on it, and I had extra details, colours as necessary. For example the red circle on the middle shield wasn’t part of the plan, but the skull in the centre looked a bit small and I needed something to fill up the space around it.
Freehand skeleton shield patterns
With skeleton shields I’ve always wavered between doing them as rusty, ruined versions of human shields or the more common emblems of skulls, bones and death. In the case of the latter, who paints them on? Imps summoned by the necromancer to give his army a touch of style, or perhaps necromantic students paint them in the evenings to finance their studies. Maybe Chaos Dwarves have a warehouse full of them that they sell to up-and-coming lich lords.
I was thinking the same thing last night as I was painting a skull on one of my shields. Who paints these on them.