I maybe one of the few Redwings fans in CA.  CSD_Salzburg's original 3d Logo (www.thingiverse.com/thing:1753540) help me create a few things for the house and Tesla (Red  of course).  I made these both with a two 18 mm x 5mm holes for magnets.

Two Designs: Both designs can utilize the PAUSE function on slicer to change filament color  to white at 8 mm.  

1.) Detroit RW Mag Inset.stl - Use slicer's pause at 6 mm to drop magnets into place.

2.) Detroint RW Magnet - Holes for magnets located at bottom to either snap or glue the two 18mm x 5mm magnets in place