This was likely a response to one or many of Count Marco's articles in the preceding days or weeks, several of which are shown on Michael Cole's Zodiac Revisited site. The July 3rd 1974 newspaper article appears the likely contender in drawing a response from the Zodiac Killer. It is entitled 'Your Mirror Can Also See Inside You' and opens with the lines "When I wrote that psychiatrists and psychologists ruined more marriages than they saved, I wasn't surprised by the angry reaction. I had contended that shrinks look at ordinary marriage problems as "cases," to be dissected, rearranged and deranged, leaving the "patient" totally disoriented."
On December 30th 2013 Tahoe27 discovered the likely inspiration behind the October 27th 1970 'Halloween' card, in the form of a Tim Holt Western comic entitled 'Redmask Meets Lady Doom and the Death Wheel.'
The links between Red Ryder, a form of cattle branding and the Zodiac Killer have been comprehensively discussed in the above forum thread.
"Red Ryder was a Western comic strip created by Stephen Slesinger and artist Fred Harman which served as the basis for a wide array of character merchandising. Syndicated by Newspaper Enterprise Association, the strip ran from Sunday, November 6, 1938, through 1965.
The first Red Ryder comic book was published by Slesinger's Hawley Publications, Inc. in September 1940, followed by Hi-Spot comics for one issue. Dell Comics launched its Red Ryder in August 1941, changing its title to Red Ryder Ranch Magazine with #145, and then to Red Ryder Ranch Comics with #149. Red Ryder Comics consisted of reprints of the newspaper strip until issue #47 (June 1947), when it began producing original material. Altogether, Red Ryder Comics enjoyed a first run, for a total of 151 issues, ending in 1957, one of the longest continuous newsstand runs in the U.S., for any Western comic." Wikipedia.
Red Ryder and Red Phantom have been explored with regards to the word "red" being present in both, however, the source of "Red Phantom (red with rage)" may lie in one person, who starred in two western films featuring an anonymous "Phantom" and "Red Ryder", both released within one year of each other, in 1940 and 1941.
Donald "Red" Barry was an American film and television actor. He was nicknamed "Red" after appearing as the first Red Ryder in the highly successful 1940 film Adventures of Red Ryder (view on IMDB); the character was played in later films by "Wild Bill" Elliott and Allan Lane. Barry went on to bigger budget films following Red Ryder, but none reached his previous level of success. He played Red Doyle in the 1964 Perry Mason episode 'The Case of the Simple Simon'. Wikipedia.
"Donald "Red" Barry went from the stage to the screen. After four years of playing villains and henchmen at various studios, Barry got the role that changed his image: Red Ryder in the Republic Pictures serial Adventures of Red Ryder (1940). Although he had appeared in westerns for two years or so, this was the one that kept him there. He acquired the nickname "Red" from his association with the Red Ryder character. After the success of "Red Ryder" Barry starred in a string of westerns for Republic." IMDB.
Did the Zodiac Killer attempt to right the wrongs of 'Count Marco', drawing on the "Red" Phantom as his pseudonym- and Donald "Red" Barry- who was "red" with rage. This western hero featured prominently in both the Red Ryder syndicate and the 'Phantom' of the American frontier.
In addition to these two movies, in the film 'Phantom of the Plains' (1945), "Red Ryder and Little Beaver return to Blue Springs and learn that the Duchess, Red's aunt, is going to sell her stagecoach line and marry a snooty Englishman Talbot Champneys, who is really Fancy Charlie, who has the nasty habit of marrying rich women and then killing them for their fortune. The concerned Red thinks everything is okay until he sees Champneys mistreating Red's horse, Thunder, and he then decides to investigate Champneys because, as he tells Little Beaver, no true Englishman would mistreat a horse. Realizing that he doesn't have much time with Red snooping around, the western Bluebeard persuades the Duchess to return to England with him, meet him at the railroad station to be married and, oh yes, bring her money with her." IMDB.
The Red Ryder connection, in tandem with the Tim Holt 'Redmask Meets Lady Doom and the Death Wheel' comic strip, both had western influences. So, did the Zodiac Killer ride into town one more time on July 8th 1974- this time as the avenging "Red" Phantom, on a mission to reprimand the irrepressible and anonymous Marc H. Spinelli.