In Windows 10 (possibly in older versions of Windows), Windows Explorer shows a "Rating" column with between 0 and 5 stars colored yellow to indicate the rating of the each file. I have a Rating field in MP3tag as well, but the two ratings seem to be unrelated. Changing the rating in MP3tag does not change the rating shown by Windows Explorer. Please advise.
See the online help on the field POPULARIMETER: http://help.mp3tag.de/main_tags.html#POPM
So you would probably have to enter an number or the right number of *.
Yet, WMP translates standard compliant entries (email|rating|play count) into the corresponding format in WMP.