Very confused about this one. It is the third watermark, making it Scott 49, ACSC 21. However, there are flaws throughout that are not completely listed in my copy of ACSC.
From a distant view, nothing special about this stamp.

The top has several flaws, including a break in the outer line, above the T in Australia. Plus a bump above the R, and a further odd right, top corner.

I've drawn a straight line at the bottom which seems to indicate a curvy bottom frame line. Per ACSC, this may be ACSC 21(3)j

Note that there may also be a line on Roo's back. Any thoughts on this one?