Based on the idea of many existing visualizers, see for instance Prusa's article for more information, but this one is based on the Biohazard symbol. See it in action on Youtube at https://youtu.be/k7Vee8Zn6uc. This is designed to work with a Prusa i3 MK3 but should work with other NEMA steppers like it has.

I planned to print the connecting rim and middle circle on the back in black instead to make them more invisible but haven't gotten a good opportunity yet. The two I've made were both printed with Prusa Orange PETG, 0.2 mm layer height.

The size as-is is a bit on the large side, I recommend printing at 70% instead, see photos for size comparison.

Print instructions

Super glue a 8mm diameter and 3mm thick rare earth magnet to the back, see photo