The Citizen Card was mailed on May 8th 1974, so this postcard was sent approximately 15 days later. The Citizen Card read in part "Why don't you show some concern for public sensibilities and cut the ad? A citizen". The Zodiac Killer supposedly wrote the SLA Letter on February 3rd 1974, beginning the correspondence with "Dear* and signing it off with "a friend", which was mimicked by the Symbionese Liberation Army on February 10th 1974, who also began their communication with "Dear" and signed off with "a friend". Then came the supposed Zodiac Citizen Card on May 8th 1974 expressing "concern" for public sensibilities and signing off with "a citizen", which was seemingly again mimicked by the Symbionese Liberation Army on May 23rd 1974, beginning their communication with "Dear" and signing off with "a concerned citizen". Two consecutive communications accredited to the Zodiac Killer bearing an uncanny similarity to two Symbionese Liberation Army communications, separated by only 7 and 15 days. Do the math. Either the Zodiac Killer didn't write the February 3rd and May 8th communications, or the Zodiac Killer was getting in on the act of writing to the Hearst Family on February 10th 1974 and making threats to President Richard Nixon on May 23rd 1974.
The Zodiac Killer was linked to the Riverside murder of Cheri Jo Bates on October 30th 1966, as well as the Riverside Desktop Poem, Confession Letter and Bates' letters. The Riverside Desktop Poem threatened murder and pronounced "Wait till next time", while one of the Bates' letters addressed the father of Cheri Jo Bates and threatened "She had to die, there will be more". The Richard Nixon Postcard contained elements of both, with the scruffy capitalized writing below evident in the Bates' letters.
In a second letter postmarked Boston, Mass on June 29th 1968 to Edward M. Kennedy, it stated "You will die if you run for Pres or VP. We hate Kennedys".
A big thanks to Rubislaw32 with his help in finding valuable communications in the Hearnap and Kennedy FBI files. Without his assistance, this article would not have been possible.