The story behind it as Mr. Page said in interview back in 1977 :
"After all this crap that we’d had with the critics, I put it to everybody else that it’d be a good idea to put out something totally anonymous. At first I wanted just one symbol on it, but then it was decided that since it was our fourth album and there were four of us, we could each choose our own symbol. I designed mine and everyone else had their own reasons for using the symbols that they used."