I like the dramatic hand and forefinger slogan in violet which was applied at Seattle USA. Similar slogans were in use in different parts of USA as well as Australia and New Zealand usually in violet.
There is also a rectangular chop in paler violet with the writing "Return for reasons and return to sender" which was probably applied at Jesselton but it could perhaps be Singapore. The writing in red would have been carried out at Jessselton GPO.
At the back, we have a very poor example of an arrival Jesselton prewar double ring postmark, probably a D24 on the Proud classification. The violet "Insufficient Address" marking was likely to have been applied at Jesselton or it could be Singapore and is the same colour as the rectangular chop on the other side. In addition, there is also the quite uncommon red hand stamp from the Dead Letter Office Singapore.
An example of an affordable USA retour postal stationary. There were different slogans in use for the different states.