Apparently the buses at this bus stop have a destination of “None”.
The addition to the sign in this case is accurate. It’s a spot where buses layover in William Street between runs.
Apparently they’ve put bus stop signs up there to stop motorists parking there if they don’t notice the Bus Zone signs. But they’ve made them old-style bus stop signs so that passengers don’t try and board buses there.
Metlink do have a design for Set Down Only bus stops; there are a few around the CBD. I wonder why they don’t use those instead — they’d probably do the job, but be less confusing.