The Collaborative International Dictionary of English v.0.48:

Placard \Pla*card"\, v. t. [imp. & p. p. Placarded; p. pr. &
   vb. n. Placarding.]
   1. To post placards upon or within; as, to placard a wall, to
      placard the city.
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   2. To announce by placards; as, to placard a sale.
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The Collaborative International Dictionary of English v.0.48:

Placard \Pla*card"\, n. [F., fr. plaquer to lay or clap on,
   plaque plate, tablet; probably from Dutch, cf. D. plakken to
   paste, post up, plak a flat piece of wood.]
   1. A public proclamation; a manifesto or edict issued by
      authority. [Obs.]
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            All placards or edicts are published in his name.
                                                  --Howell.
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   2. Permission given by authority; a license; as, to give a
      placard to do something. [Obs.] --ller.
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   3. A written or printed paper, as an advertisement or a
      declaration, posted, or to be posted, in a public place; a
      poster.
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   4. (Anc. Armor) An extra plate on the lower part of the
      breastplate or backplate. --Planch['e].
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   5. [Cf. Placket.] A kind of stomacher, often adorned with
      jewels, worn in the fifteenth century and later.
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WordNet (r) 3.0 (2006):

placard
    n 1: a sign posted in a public place as an advertisement; "a
         poster advertised the coming attractions" [syn: poster,
         posting, placard, notice, bill, card]
    v 1: post in a public place
    2: publicize or announce by placards [syn: placard, bill]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "placard":
   advertise, affiche, ballyhoo, bark, bill, boost, build up,
   bulletin, circularize, cry up, establish, give a write-up,
   give publicity, handbill, plug, post, post bills, post up, poster,
   press-agent, promote, publicize, puff, sell, spiel, write up