Another Led Zep question

Does anyone know what the word "Zoso" means? It's Jimmy Page's symbol that first appeared on the fourth album along with the other band members'. I read that it has something to do with mercury but I think that's not it.

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-Dave

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"Life is infinitely stranger than the mind of man can imagine."

- A. Conan Doyle

The band never gave an explanation for it. It was part of their protest against commercialism; they wanted to produce an album with no information on the cover.