In the UK 0000 is used when level information is unreliable. When I was trained it was called "alpha midnight", I've never seen it used live.
However, yes I think using 0000 when you're shutting down is wrong.
I'm actually not sure how 0000 is treated by the radar system but in theory I could see it overriding ATC level filters (as it's supposed to use for traffic with unreliable level reporting) so if that is the case then setting it before parking could in theory cause your target to appear on area displays. I have no idea though if that is how a 0000 code would be treated or not.
Perhaps someone with more area and technical experience could add in some more info.