The first two units are "Grenzschutz" units. So it is the Grenzschutz Nachrichtenzug (mot) 12 - Because Höh.Kdo.(z.b.V.) XXXIV. evolved from Grenz.Schtz.Kdo.12.
The second is a Grenzschutz Kradzug 312.
The third "Lyra" symbol is a military band.
G = Grenz- (Border)
The XXXIV. Armeekorps had been raised from Grenzabschnittskommando 12.
The 300 series of numbers was allocated to the border troops. Hence the 312.
The unknown symbol is for the band.
For a listing of the symbols, see the various buttons under Fact Files there.