Ron, there are 6 non-government factories listed as manufacturers of 25 Pr No. 1 Mk II primers in Australia during WW2:
B.K.M. Co, Sydney, NSW
Geo. Hill, Western Australia
Toowoomba Foundry, Queensland
Kelvinators, Adelaide, SA
Henry Jones, Hobart, Tas (monogram IXL/T)
Electricity Meter Manufacturing Co, Sydney, NSW (Emmco)
My guess for the monogram you show is the Toowoomba Foundry as it was known as the Southern Cross foundry which explains the S with a cross.
Southern Cross Foundry Pty Ltd, 251-257 Ruthven St, Toowoomba, Qld.
I have a few primers with this maker also.
Graeme