I surfed a little on the net and then opted for a rather simple solution. I downloaded some samples and printed them on a transparent sheet. Then I cut three stencils with Xacto knife and sick them on the half track. I masked it carefully and used the airbrush loaded with white color: the result was quite good although since the stencil did not adhere fully I needed to refine the star manually a little. Next time I think I would use adhesive paper that sticks better to the surface to be painted.
To see the stencil and the results ...
the stencil for the front of the M3. As you see it does not perfectly stick to the surface
The result after airbrushing with white.
The stencil for the M3 door and the result