We've all seen the "Peek through the Pines" postcard allegedly sent by the Zodiac back on March 22, 1971: Whomever prepared the postcard attached to it a portion of an advertisement for a housing development at Lake Tahoe called "The Pines." Here are all of the pages of the advertisement. Note in the third image all of the crossed-circle symbols. Click for larger view: I think whomever was responsible for sending the postcard saw all of the crossed circles and couldn't resist using it.