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
See here my other rotation indicator designs including some more instructions, videos and links
Enjoy and don't be shy to post a made one!