Definition from Wiktionary, the free dictionary
placard (plural placards)
- A sheet of paper or cardboard with a written or printed announcement on one side for display in a public place.
a sheet of paper or cardboard
- To affix a placard to.
- To announce with placards.
- to placard a sale
placard m (plural placards)
- A cupboard, cabinet or closet built against or into a wall.
- An ad that is felt to be injurious, seditious or in otherwise bad taste.
- (dated) A placard.
Usage notes 
- The use of placards for announcements by authorities having mostly disappeared, the word affiche frequently replaces it in that meaning.