This is the most exhaustive explanation I could Google up:
What do the four symbols mean?
John Bonham
From the Led Zeppelin InFrequently Murmered Trivia List:
Bonzo’s symbol from the fourth album, the three linked circles came from the same book of runes that Jonesy’s came from, and is meant to symbolise the man-wife-child trilogy. Bonham’s symbol has a common elements with Jones’s, trisected ovals, or “yonics”, which are in opposite aspect in their symbols, reflecting that they symbolise two very different people. Plant has pointed out that it also looks like the emblem for Ballantine beer. Another source says that Bonham picked the symbol at random, simply because he liked it, and it reminded him of drumheads. A DJ in Britain, Danny Baker, came up with the interesting theory that Bonham was sitting in the pub with his customary glass of the amber fluid and plonked it down on his beer mat a couple of times and noticed what a nice little symbol the marks formed. Jason Bonham has said, on the same DJ’s show that the symbol is the man-wife-child trilogy rune. The German company Krupp AG also has a symbol with three interlocking circles, although it is the opposite way up to Bonham’s. A German band called the Krupps has used this symbol and pictures of zeppelins for album art. Another reasonably plausible thought, is that the symbol looks a bit like a drum kit when seen from in front, with bass kickers, or above with toms and cymbals slightly overlapping.
John Paul Jones
From the Led Zeppelin InFrequently Murmered Trivia List:
Jonesy’s symbol from the fourth album was taken from a book of runes and symbolises a person with confidence and competence. It shares the common characterisitc with Bonham’s symbol of having trisected ovals, termed “yonics”, which are in opposite aspects on the two symbols, indicating that the two symbols reflect two very different people.
Robert Plant
From Led Zeppelin expert Thor Iverson:
Robert’s symbol is the Feather of Ma’at (the Egyptian goddess of justice and fairness) and the emblem of the writer. It is the latter to which Robert was probably referring when he suggested that people looking for the meaning of his symbol “…look it up in a suitable reference work.”
Jimmy Page
The origins/meaning of Jimmy Page’s symbol has been dubbed “The Holy Grail of Led Zeppelin Trivia”. After much research, Thor Iverson reported the following:
…A disclaimer: while I respect the validity of the interpretations I am about to present, I should note for the record that I do not believe in the religious, mystical, or symbolic meanings therein. For me, it is strictly information–but I will present it as given to me, with these factors taken into consideration.
Our task was this–examine the symbols on IV, Jimmy’s Outrider logo, the symbols down his black '75 tour pants, and the hand drawings on the No Quarter cover. We have approached reasonable closure on some of them, but others (especially Jimmy’s symbol) remain unfinished. I am posting what we have now as a way to stimulate further research by others, and to suggest avenues of exploration.
No Quarter was fairly easy. The spirals on the woman’s finger become more complex as they move closer to the hand itself–signifying the development of femininity. The spirals’ increasing detail means they are moving closer to the wrist chakra.
Jimmy’s Outrider symbol may or may not be anything other than a stylized “JP.” We’re still working on this one.
Jimmy’s pants symbols–headed by Jimmy’s IV symbol, these may be simple astrological signs (“69,” for instance, is the symbol for Cancer) or something more complex. Again, this has been given a lower priority in comparison to the infamous “Zoso” symbol.
JPJ’s symbol (usually given to mean a person who is confident and competent) and John Bonham’s symbol (the man-woman-child trinity) have something in common–trisected ovals. These “yonics” are in opposite aspect in the symbols, which indicate that the symbols themselves are opposites (interesting, since that was probably not intended when they selected them). While the two were the closest in a musical sense, if one examines their personalities one will see that they were indeed quite different, and this matches the symbology on IV.
The two symbols on the outside (Page’s and Plant’s) are, in typical magical fashion, the stronger symbols–the stronger symbols are set on the outside to protect the weaker ones.
Robert’s symbol is the Feather of Ma’at (the Egyptian goddess of justice and fairness) and the emblem of the writer. It is the latter to which Robert was probably referring when he suggested that people looking for the meaning of his symbol “…look it up in a suitable reference work.”
Page’s symbol, as a self-designed glyph, could have any number of meanings depending on how he used and combined the symbols and parts of symbols, and from what traditions he took the symbols themselves. I will present all the possible interpretations we have, but one set of them seems more likely than the others, and will be given slight precedence at this juncture (it is
also the interpretation I judge to be the most likely, so consider that when making up your own mind).
All of the symbols in “ZOSO” are parts of the incantation for opening a magical circle. This may or may not be relevant, but it is interesting.
“O-O” is a vesica piscis (for reference, the genitals of the mother goddess and the beginning of life). On the Chalice Well at Glastonbury, this symbol appears closed on the lid–the two circles intersect. In that case, the symbol is designed to protect spiritual secrets. Thus, the seperated circles suggest that this symbol now represents the revelation of spiritual secrets. The Sufi interpretation is similar: knowledge of creation. Other possible interpretations include east/west or a cord. A further meaning is somewhat disturbing, especially to our sources: it could signify eternity. The meaning of eternity in magical symbology is important to black magicians, for with the full understanding of eternity they believe they can open the door to hell. This meaning doesn’t really fit in with the other interpretations, but I had to present it.
The “S” that seperates the “O-O” symbol might be the symbol for Samhain, the Wiccan sabbath. This is the night when the veil between the living and the dead is broken down, and the spirits of both can pass through. Less likely: it symbolizes water.
The “Z” that heads the symbol usually signifies sleep, the subconscious, or death. So far, then, we have the revelation of spiritual secrets from the dead, or a near-death or deep-sleep experience. Less likely: it stands for smoke.
The long sweeping line at the bottom of the symbol means almost the same thing no matter what tradition is examined. In ancient Egyptian, it means the opening of the way, or the sum of all things in the universe. In Sufi, it literally means God (in this tradition, God is everything including one’s self). However, the Leyden Papyrus gives a further meaning–a magical blade used to call Anubis and raise the dead or conjure a spirit. All three of these meanings agree with what we have found so far.
Trying to decipher the little hook on the arm, though, presents a whole new range of possibilites (ones that also affect the meanings of the “S” and “Z” characters). It is possible that the hook is the Hebrew character zeyin, meaning weapon or sword (or Jimmy’s guitar?) The symbol could mean the natural flow of time. It is also possible that it represents St. Andrew’s cross, a boundary sign used by the Romans to indicate the unification of the upper and lower worlds. It is also possible, and in fact likely, that the hook, “S,” and “Z” could represent swastikas. Not in the Nazi usage, but in the ancient meaning (from the Isle of Man, for the sea-god Manannen–this was co-opted by early Christianity to represent the power of Christ).
If so, then the hook could represent fire, but they could also represent the interlaced swastikas the Druids used in their mystic knots (two S’s meant two arms and two legs, two Z’s meant fire and/or lighting). The final possibility is the most intriguing–that they represent sex. If so, they would represent Tantra, the practice of Tantric sex (hyper-extended sex without orgasm or release). Crowley devotees will note that this was something Crowley was interested in, and thus it would make sense that Jimmy would know the usage.
So the final first-approximation guess we have is this: a near-death or Tantric sex experience (for the trance-state of the latter would be designed to reach the subconscious anyway) to unify the worlds of the living and the dead, and thus to reveal the secrets of the universe.
Eeeesh!!!
sweet bike 
very nice.
