I started by printing the basic NEMA Windmill motor rotation indicator but I was underwhelmed, so I printed it at 200% scale and felt much better but it still seemed too small and chunky - especially after looking at pictures of Dutch windmills where the blades almost touch the ground as they rotate. So I sat down with the picture included above and estimated how big the blades would need to be if the printer extruder motor and extruder housing were a Dutch windmill. This is the result. Note that in order for the blades to rotate in the real world they need to be covered with something like canvas sail cloth. Without the cloth, the blades don't rotate, but I wasn't going to take the time to put cloth on my printer blades just for realism... So I have a second model with a 0.2 mm layer that is supposed to represent the cloth covering (though only on one side). You will need to use two of the magnets referenced in this article (https://prusa3d.us5.list-manage.com/track/click?u=fc132da4017f47b701012d494&id=3ca54333be&e=97e2e126c7), One fits just inside the motor housing and the other is super-glued to the blade. I put a small circular indent on the back of the blade center to aid in placing that last magnet. Unfortunately, Dutch windmills rotate counterclockwise while printer motors rotate clockwise so it's not completely realistic - but not bad.
NOTE: THIS DESIGN WON'T WORK WITH THE "ANGLED PRINT FAN" CONFIGURATION OPTION
Note that the blades are wider and taller than the extruder so be sure you have clearance for them to turn - especially on the right side of the printer as viewed from the front.