>>12065080It's the Eureka flag, which was flown at the battle of the Eureka stockade which has some significance (I don't know the story that well) to the CFMEU.
The southern cross tattoo often indicated membership in the Knights of the Southern Cross, which is an Australian offshoot of the KKK, but it's pretty much defunct as an organization so people just get them as a symbol of Aussie pride.