Clear arrival postmark for London.
2c green with a " Micky Mouse" type mark with the letter R on top, some sort of return letter mark perhaps. I assume it is of UK origin but I could be wrong. It is not like any postage or fiscal marking for NB that I know of.
Update It looks like part of a "registered London E O" cachet that I have seen on an Oswald Marsh envelope.
Probably not of UK origin but still very interesting to look at.
Update It is a "Killer" oval duplex cancellation from USA with the example on cover as shown below. It cost me a fiver and I wonder how much a good cover like this would sell for if it were NB.
A very nice clear arrival cancellation for Brisbane, Queensland, Australia.
Wavy line killer cancellation likely to be of GB origin but a smaller version was also used in the Straits Settlements.