The trigrams referred to in the episode are from the eight diagrams of ba gua, a part of Taoist philosophy. No trigram matches the one drawn throughout this episode, but zhèn (☳) comes the closest. Ironically, its meaning is nothing like 'peace'; the meaning is closer to strife or division or revolution.
This episode borrows heavily from a popular theme of the era, the idea that a soldier may be taken, brainwashed, and returned to carry out some mission counter to the interests of his command. The best example of this is probably Frank Sinatra's character in The Manchurian Candidate (1962). The term came into vogue shortly after the Korean War, the concept used to explain why certain American prisoners apparently defected to the enemy side following capture (making anti-American statements, for example). It is far from certain that brainwashing is a reliable way of producing unaware "sleeper agents". The more likely result of the techniques used to brainwash an individual would be short or long term psychological harm of various kinds, not obedience to an external will.