A historic plaque is a sign affixed to a built object or displayed in public view on its grounds or interior, which presents interesting information about the structure's history, architecture, or related topics.

The plaque must feature some informative data or text other than the name, address, involved companies, or some award or certification received by the structure. A plaque recognizing certification as a historic landmark does not count unless it also contains texts or data about the structure itself (not just about the awarded certification).

The information must concern the structure or a related topic beyond identification or an award alone. A historic-landmark marker qualifies only when it also contains substantive information about the structure, whether displayed outside or in a publicly visible interior location.