How are backlit aircraft panels (for simulators) made?
This video says the following:


  Here's my Tonson TS-3040C CNC making an EFIS panel for my flight
  simulator. For the lettering I am using a 0.4mm End Mill and for
  cutting out I'm using a 1mm End Mill. RPM is 10000 and movement is
  300mm / Min. The material is Cast Acrylic which I have given one coat
  of black paint and two coats of grey paint.


So that's at least one method, but there are probably more...