Hi there

I bought this stamp recently 5c on 8c Buff Hong Kong after I noticed that the Barred Killer obliterator was not the normal HK or Treaty Port, but clearly says GPO running 90 degrees to the stamp. I have a Brisbane GPO cancel on an HK stamp but it is an horizontal rayed obliterator, so the question is where is this GPO killer from. It looks a bit like the GPO killers from Perth Western Australia - is it from Perth or is it from somewhere else?