The peace symbol ( ☮ ) was a graphic image created on Earth in 1958 as symbol of the nuclear disarmament movement. It was later adapted by the anti-war movements of the 1960s.
During the 1970s, Roberta Lincoln wore a universal translator disguised as a peace symbol pendant while visiting East Berlin. (ST - The Eugenics Wars novel: The Rise and Fall of Khan Noonien Singh, Book One)
During the Third War, the peace symbol became the symbol of the underground movement, as a way of identifying safehouses. As peace became widespread in the decades that followed, the symbol fell into disuse.
In 2045, just before his death, Professor Jeremy Grayson gave a peace symbol medallion to a temporally displaced Spock, to identify himself as Grayson's emissary. Just before returning to his present, Spock buried the medallion in Thebes. Returning to Egypt in 2284, he rediscovered the symbol not far from where he had left it. (TOS novel: Strangers from the Sky)