1. 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.
2. A written or printed paper, as an advertisement or a declaration, posted, or to be posted, in a public place; a poster.
3. The two most common placards in general use on vehicles are for the handicapped tags for personal automobiles, and hazardous materials warning signs for commercial vehicles.

There are other types of placards; for examlple, the wide load signs used when mobile homes are transported on a street or highway.