UPDATED - Disregard - The watermark is NSW.
Good Morning,
I have a strange New South Wales 5d stamp which I can't match the watermark for. The watermark looks like an S or an 8 in a shield under a crown from what I can tell. Also the stamp has a perfin but I'm not sure for whom or what it reads. Perf 11.5 x 11.
Stamp Inverted:

Front:

Thanks for looking