I thought the title was Led Zeppelin IV (4)? Also known as the "Rune" or "Zoso" album.
The Zoso symbol chosen by Jimmy Page as his symbol for the 4th album cover was originally written down by a 16th century hermeticist J. Cardan in a classical 1557 work Ars Magica Arteficii.
You can see the symbol in the book "Dictionary of Occult, Hermetic and Alchemical Sigils" by Fred Gettings, published in 1982 by Routledge & Kegan Paul, ISBN 0-7100-0095-2. This book also tends to go wandering from libraries due to interest from folk practising witchcraft, but I was able to interloan a copy through my local library without too much difficulty.
In the section "Planetary Symbols" on page 201, under Sigils, for planet Saturn Cardan's 1557 symbol is virtually identical to the Zoso symbol above (and nothing else in the occult dictionary is even vaguely similar).
Jimmy's astrological sun sign is Capricorn, which is ruled by the planet Saturn. Cardan's symbol above is a magickal symbol for it. This symbol was also the magickal symbol for Austin Osman Spare.
Some people have referred to this symbol as being in the "Red Dragon".
http://www.inthelight.co.nz/ledzep/zososymbol.htm
And now you know your Zoso avatar a little better.