The marking is very faint and does not show up on this scan. I can make out ..gistrate of the S... I think it could be (ma)gistrate of the S(andakan court)
It looks like a registration cancellation but is bigger than any of those illustrated in Ted Proud's book. On the other hand being light blue, could it be fiscal? It could be another magistrate court marking.
Update It is a larger version of Jesselton R11, fairly rare as in use 1931-1932. linda1983my has provided much much better example as above.
There is a faint "R" in the centre of the image. The postmark corresponds with the cancellation Sandakan Parcel Post. These postmarks are rarely seen. I hope to be able to replace them with better looking specimens in the future
Update It is Sandakan Parcel Post PP3, rare and used between 1931-1932. Again linda1983my has a good example as above. Where and how does one get this stuff???