I cut the lettering into the sideframe cavities the same way i cut the sideframe cavities themselves. I had a bench top CNC milling machine and except for two store-bought ball end mills made all my own cutters myself with a Deckel SO cutter grinder using fine-grade carbide 1/8" diameter cutter blanks. These were ground into 4-sided tapered flat bottom cutters.
The challenge for making the cutters to cut the lettering cavities was the small tip size--.0025" diameter. Accuracy was found using an optical comparitor and if under size the cutter was used for roughing. All this required steady hands and very good close-up eyesight, neither of which I have anymore.
