In case anyone else was wondering, that flag is an unofficial flag design for 'Greater Sydney': https://www.crwflags.com/fotw/flags/au-ns-gs.html

The Saint George Cross with the superimposed Southern Cross comes from the 'National Colonial Flag': https://en.wikipedia.org/wiki/National_Colonial_Flag

No idea what the political implications of it are, but the cookers love to spout off bullshit about archaic laws of some kind, so the colonial connotations probably tie in with that.