(I'm pretty sure it's constitutionally mandated that any text about crafts that involve stones must include the use of the word "rocks" to mean "is amazing.")
I am a beachcomber. Along shorelines and stream beds, I am usually looking down, searching for rocks that have an interesting shape, pattern, color, or smoothness. A lot of the stones I pick up end up decorating my houseplants, but some of them end up in my craft work. Earlier, I posted links to ten crafts you can make with rocks, and here's my contribution.
Painting and drawing on stones is not a new idea, but I put my own twist on the finished product but turning my decorated rock into a pendant you can wear.
So anyway. You can stick with a plain white design, like these geometric shapes:
I've found that I can use regular fine-point Sharpies over the dried Montana white — there's no need to buy a rainbow of expensive paint markers. Once I discovered the level of detail I could get, it opened up my design options. I ended up creating a couple of simple animal cameos. Here's a series of photos to show you the order in which I added the elements and layers.