I’ve stumbled upon this curious http://grangevillegolf.com/idaho-golf-clubs/womens-league/ GPO Sarawak handstamp mark in eBay after years of not seeing one. The last one I saw was from many years ago on a cover similarly franked with the stamps from the 1947 issues. Unfortunately, I don’t have a picture of that cover saved.
This one was sold in eBay mid-June 2016 and ended at a final price of US$51.21 after 9 bids.
The violet-ink handstamp was applied on the top right corner on a cover addressed to USA. There was no markings at the back. The cover is franked with various Sarawak stamps from the 1947 issues (1¢-4¢) and tied by Proud’s D31/32 postmarks.
I could not find any mention of this handstamp mark either in the Sarawak handbook by Forrester Wood or Proud’s book on the postal history of British Borneo.
Perhaps someone may be able to shed some light? Comments appreciated!