Tony, thank you! Now I see where I blundered!
As at 15 Dec 1942 10/48 Inf Bn were part of 3 Inf Bde (not 23 Inf Bde: my misinterpretation of the original instructions. To be fair, they are pretty badly presented.). 3 Inf Bde were the senior Brigade at that time, consisting of:
27 Inf Bn Veh sign 50
43 Inf Bn, veh sign 99
10/48 Inf Bn, veh sign 53
all of which had a red background. (E Coy is no longer relevant to the 10/48 markings story, as they had transferred to 19 MG Regt.)
The battalions in 23 Inf Bde at that time had a green background (7, 8 and 2/4 Pnr Bn) and 19 Inf Bde had a brown background (2/4, 2/8, 23/21 Bns).
When 10/48 Inf Bn was moved to 23 Inf Bde, they were allotted the unit sign 93 on a Green background, as per NT Force GS Instruction 37 of 6 April 1943.
So:
10/48 Bn Dec 42 to March 43: 53 on red. (part of 3 Inf Bde).
10/48 Bn March 43 till Sept 43: 93 on green (part of 23 Inf Bde until end Sept, then became part of 2 Inf Bde, then in July 1944, moved to 12 Aust Inf Bde)
Formation sign: Buffalo on boomerang from Jan 43 onwards.
Thank you.... I think we have it sorted!
Pity Graham Mck-Smith only produced the two volumes, they are excellent references. His original intention was to produce volumes to cover the entire mainland, but I've not seen anymore than V1&2: have you?
Mike