I was recently asked to explain this destination on Johannesburg 60 by a German visitor. It means that the minimum fare payable on the particular journey is six pence or 6d. South Africa together with other British Commonwealth countries (except Canada) used the Pound Sterling currency which was divided into 20 shillings and the shilling was divided into 12 pence.
In Johannesburg high minimum fares were charged on some longer distance cars leaving the city in the evening rush hour.
2 & 3 Glasgow 812 and Leeds 180 seen from above. (Leeds 345 was the other service car).
Photographs taken somewhere in England.