It's not often that we see the women of Mad Men in T-shirts, even when dressed down, so it was a little jarring when, in the most recent episode's final scene, Megan is wearing a white tee with a big, red star on it. It almost seemed anachronistic, but not only was it accurate for 1968, it was "no coincidence," according to costume designer Janie Bryant, that it was the same as the one Sharon Tate wore for a 1967 Esquire spread.
Much of season six has been about not only the deterioration of Don Draper and his marriage to Megan, but also that of New York City, which is becoming less and less safe. The Drapers' apartment was burgled, Peggy's boyfriend Abe was attacked coming out of the subway, Megan mentions a shooting in Central Park, and emergency sirens—increasing in volume as the season progresses—are now furniture in the aural sets. Additionally, police cars, and some kind of commotion, are featured in the background of the colored pencil promo illustration for the season. (As is a Don Draper doppelgänger, which fits in with the "two halves of the same person" motif that Megan is dealing with her twin roles on her soap, and that Peggy pointed out about Don and Ted Chaough. Also, this episode was titled "The Better Half.")
Others have pointed out, that Megan's costumes have mirrored that of Abe's throughout the episode, and that the red star on the white T-shirt might reflect when Peggy stabbed him, and could be an ominous sign that Megan is next up to be on the receiving end of some violence.
But Matthew Weiner's trademark is his ability to totally fuck with his audience. (The final scene of the last episode of The Sopranos was dripping in dread, but nothing happened—that we saw.) While costume design on Mad Men has been as deliberate and layered as the writing on the show, the red star could also be a red herring. After all, Tate wasn't murdered until 1969, but something else happened to her 1968—she got pregnant just as her acting career was taking off.
While Megan already confessed to Sylvia that she had become pregnant and had a miscarriage earlier in the year—admitting that she was relieved because she the timing wasn't right for her burgeoning soap stardom—she also told Don in this episode's final scene, while wearing that Tate tee, that something needed to change in their relationship. She wouldn't be the first to believe that a baby could save a marriage.
Mad Style: The Better Half [Tom and Lorenzo]