This is a Sarawak 1961 OHMS, or ON HIS/HER MAJESTY'S SERVICE Cover sent locally from Kanowit to Sibu on 11/23/1961.

This guy has a couple things that make it really special.  First is the BORDERED BOX KANOWIT OFFICAL POST PAID in RED.  It is also Circle endorsed, and signed: DISTRICT COURT KANOWIT CDS.  These are RARE local markings!