That watermark shows the small gap between NSW and the crown.
On the scan it looks like the yellow-green shade, so SG 327c.
No research (yet) from collectors on frequency of watermarks in this thread
https://goscf.com/t/67868&whichpage=3 .
The 2004 ACSC provides no listing for inverted (only) watermark on perf 12x11 (ACSC N23) but a large premium for 'reversed' or 'reversed and inverted' watermarks.