Following the mixed response to “Led Zeppelin III”, Jimmy Page suggested to his band mates that instead of an album title they feature four symbols representing each of them on the cover. The audacious move paid off with the album becoming one of the best-selling albums of all time. “We decided that on the fourth album, we would deliberately play down the group name, and there wouldn't be any information whatsoever on the outer jacket,” said Page who designed his own symbol, which looks like the letters ZoSo. Though he has not given any explanation of what it means, he said it was not intended to be a word. Both John Bonham and John Paul Jones picked their symbols from the Book of Signs by Rudolf Koch. Robert Plant's feather symbol was his own creation, based on the sign of the Mu civilisation. There is also a smaller symbol chosen by Sandy Denny who sang on “The Battle of Evermore”.