OK, I think it is beginning to dawn on me what you are doing. You have a schematic, not just lettering, and this has to be placed on a label made of Traffolite in the 3D model. Further you want the label visible in the assembly as well as the drawing of the assembly.
First off, SW really won't allow display of a 2D sketch onto a face in a 3D model. For one thing, in the 3D environment a line has no width and so it wouldn't show up. If you want a lot of work you could thicken the lines and cut into the Traffolite. It might take several sketches because of the fact that a schematic does not necessarily have "legal" geometry for SW to extrude a cut.
A second method more ammenable to a production environment would be to mark off on the 3D model and area where the label is to be affixed and reference the lable on another drawing where only the label graphics appear. The drawing of the 3D model would specify size and location of the label and the label drawing would specify the graphics to go on the drawing, perhaps in a format that an engraver could use like dxf.