The 'V' peace sign was prominent in the American national consciousness at the time of the publication of Gravity's Rainbow. President Nixon had made the gesture his trademark when he ran for President in 1968. At the time of the novel's publication, Nixon was facing increasing pressure over investigations into his role in the Watergate scandal. Pynchon's inversion of Nixon's trademark gesture is a tacit condemnation of the President, following on from his quotation of Nixon in the epigraph to Section Four of the novel.
Nixon would end up resigning from office the following year, 1974. His last act as President before boarding the Marine One helicopter to return home was to turn to the crowd and give his 'V' salute one last time.