Hello,
the numbering of the units of specialists (Motor-HJ, Flieger-HJ, ect) always starts with the number 1 in their specialty :
1. (Motor-Gef.) / Bann 173
1. (Flieger-Gef.) / Bann 173
1. (SRD-Gef.) / Bann 173
...ect...
and, of course, it is also the same for the basic HJ (Stamm & Allgemeine-HJ) :
1. (Gef.) / Bann 173
On the flags, since 1938 (if I remember well) the speciality is recognizable with the color of the background of the patch and the color of the inscriptions and the braid. Before the colors meant something else.
Best regards