Just another design for an extruder rotation indicator/visualizer. Print, glue a 8x3mm Neodymium magnet to it and snap it onto your extruder motor.
I have used CorrugatorSupercilii's OpenSCAD Turbine Propeller Generator to generate the propeller (https://www.thingiverse.com/thing:2187837)
See here my other rotation indicator designs including some more instructions, videos and links: https://www.thingiverse.com/thing:2638857
Enjoy and don't be shy to post a made one!
This one might be a bit more challenging to print considering the overhangs and thin walls. Go slow and make sure to have enough cooling. < 0.2 resolution is recommended.
The one in the picture is printed in 'Prusa Orange' ABS