Don't spoil his fun - next you will be saying that the ones marked D3D. D4D etc went to the 3rd and 4th military districts
A post from our 'aussie friend' Damien on the same subject.
I'm pretty sure that the numerals between the D _D refer to the MD number. I have seen D/I\D on 6, and we did not have 6th grade reserve arms.