Censor cachet

This interesting 2c 1941 war tax stamp has 2 separate cancellations. There is firstly an oval company chop from Harrisons & Crosfield at Sandakan. Superimposed on it we have a triangle with the number 15 within and the word "censor" on the right side. This is a pre WW2 type handstamp which was applied after examining mail going overseas.
Even though the number 15 was allocated for use in Sandakan, this is unlike any of the recorded censor chops that were in use in North Borneo which broadly consisted of two types. They were rectangular or triangular and the latter were double sided with the wording enclosed between the two lines.
I have been reliably informed that this single sided triangle is similar to those used in India. Some further research brought up two possibilities. They were the "field censor" and the "passed censor" chops. The latter type usually has the name of the city just underneath eg Calcutta. This is likely to be the " field censor" chop which would implied it was used by the armed forces.
So what is the story behind the use of this stamp? It would seem that a letter of a commercial nature was sent from H&C at Sandakan, North Borneo to an army personnel in India. The cover would have borne the censor cachet of North Borneo. It was further scrutinised in India where this cachet would have been applied. Or quite possibly, the letter was rerouted to the addressee who has left for Britain and was subjected to this further censor procedure.

Update I have a very good suggestion that this censor could be from Hong Kong. Given the strong commercial links between Hong Kong and Sandakan (used to be known as "little Hong Kong"), this is very feasible. India would have been an unusual destination. But I think we are all agreed that this is a most unusual stamp. However having done a quick search on the internet, the triangular "passed censor" cachets I have seen for HK so far has the words within the triangle and also "Hong Kong" at the bottom. There was one with the letters on the outside of the triangle. It also has "Hong Kong" just beneath.  I shall update if I have any further information.

Further Update I have been sent detailed information with regard to both HK and Indian censor cachets. This is almost certainly a Hong Kong Type 5 censor which was in use between September 1940 and November 1941 and was available in violet, green and red. The length of the wording on the side looks more compatible as well as the dates of use. There is still a remote possibility of it being an Indian "field censor" cachet but I think it is highly unlikely. This is the limitation of a single stamp as compared to all the details available on a used cover. But I have had fun with all the detective work. My thanks to GE-KK for providing scans and information.

Further Update I think this is from a censored commercial document and not a postal cover. Hence no post marks, local or arrival or otherwise.

Labuan centenary handstamp

Note small"4" in "24TH"

This was a fixed date hand stamp used to commemorate a hundred years since the island was originally given away by the then Sultan of Brunei. He actually agreed to officially cede Labuan on 18 December 1846. But the British flag was not raised in Labuan until 24 December of that year. It is the later date which was used in this hand stamp. It is rather surprising that the example in Ted Proud's book showed a date of DEC 22 which also left out the "TH".
The hand stamp was said to be in use for a month but in Robson Lowe' book mentioned one week. The majority of existing covers were dated 24 December 1946 and were invariably philatelic. Other dates are hard to find. The chop was valid for use on the BMA stamps of both North Borneo and Sarawak. But examples on Sarawak stamps are fairly uncommon and well worth looking out for. The use of this hand stamp on Australian stamps and covers are a bit of a mystery as stamps from Australia were only allowed to be used immediately post war before the availability of BMA overprinted stamps. They were philatelically inspired and there must have had been some laxity in the post office services in those chaotic times.