About four years ago, my wife and I we bought our first 3D printer an we started to tinkering with Sketchup. These medallions (inspired by one of the greatest video games ever) were made with a 3D design knowledge close to zero, but we still love them.
They are very easy to print, add about 20% infill to ensure a good floor to build a good surface for each symbol. What I do in simplify3D si a two process print, the first part has 20% infill, the second part 0%. If you don't know how to do it, just use 20% infill.
I use 0.3 layers.
Do not sell my designs or the resulting 3D parts, it's stupid to get into legal trouble.