For the model with magnets, you need five round 10mm x 1mm strong magnets (neodymium). The model I printed is the one with magnets, so I can use it as a stand or as a fridge magnet.
You can import the STL directly into the slicer and arrange it on the sign model (might need a NetFabb repair). or Import it into FreeCAD with the provided FCStd-File. It should be at the right position without any further transformation, convert it to shape in Part Workbench, and make Refine Shape. Export it togehter with the other parts as 3MF.
In the slicer, add a pause for the insertion of the magnets on height 1.6mm (layer 8 with 0.2 layer height)
Add a color change on height 3.2mm (layer 16 with 0.2 layer height).