placard
noun [ C ] uk/ˈplæk.ɑːd/ us/ˈplæk.ɑːrd/
布告;标语牌
a large piece of card, paper, etc. with a message written or printed on it, often carried in public places by people who are complaining about something
Demonstrators marched past holding/waving placards that said "Send food, not missiles!" 示威者举着／挥动着标语牌游行，上面写着“要食物，不要导弹”。