This is a new find of a previously unrecorded item which is of historical and philatelic importance. It is quite heartening in this day and age that such material can still be found. Earlier items may still await discovery. The last word in philately is definitely not written!
Bearing in mind that the first stamp of North Borneo was issued sometime in March 1883, this is a very early item indeed. The earliest date for this "Eight Cents" surcharge is given as June 1883 in the Stanley Gibbons Catalogue which now can be updated to 21 April 1883 or earlier.
This is a pen cancel as the first postal canceller for Sandakan did not appear until January 1884. The scrawl "skan" at the top was for Sandakan. More importantly, there is a clear dumb cancel from Singapore to confirm postal use as pen cancels were also used fiscally. Eight cents was the rate to the Straits Settlements.
The writing has some similarities to the first postmaster Captain Edward Richard Connor who was also harbour master. A sample of his signature is given above. A very detailed write up in 3 pages is now in the current issue of The Sarawak Journal. But you can see the picture of this very important item much much better here.
Prior to North Borneo, he served in the Royal Navy, being an Englishman who was born in Kent in 1848.
After leaving North Borneo in 1885, he joined the Naval Brigade in New South Wales, Australia. He died unexpectedly shortly after retirement at the age of 57.