This billboard appeared on Sunset Boulevard in Los Angeles, 1971.

Nobody really knew what these symbols meant.
 “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.”

— Jimmy Page