I bought this single stamp from a seller in Canada.
It’s the highest value stamp (10 shillings) in the series known as the 1927-1930 London Pictorials; the last South African stamps printed in London.
(After that stamps were printed in South Africa).
The Afrikaans-English se-tenant (joined) stamp pairs are very expensive (up to $200), but the single ones are $10 or so.
I’m still looking for an English one with ‘SOUTH AFRICA’ inscribed at the top.