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Reportedly there was an earlier spotting of the symbol on the 1960 hardcover edition of Dietrich Bonhoeffer's book Ethics. I have not been able to find it.
This source says it probably a much older symbol, possibly of Lutheran Origin. The Latin means "Christ the King".
It depicts a Crown of Thorns on the Cross, which is over the world. The world is partly distorted/unfinished to represent the lack of satisfaction this temporary place brings. In some instances a drop of blood can be seen, representing Christ's blood covering the world in grace.
If so, one might think of it as a vertical rendering this the symbol, below, with the addition of a circle representing the world.:
I cannot vouch for the above, but it makes sense.