Both Uses of

plaque
in
1984, by Orwell

The voice came from an oblong metal plaque like a dulled mirror which formed part of the surface of the right-hand wall.†
p. 2.1 *

Any sound that Winston made, above the level of a very low whisper, would be picked up by it, moreover, so long as he remained within the field of vision which the metal plaque commanded, he could be seen as well as heard.†
p. 3.1

Definitions:

(1) (plaque as in: a plaque on the wall)
a tablet with information or a message made for placement on a wall or other object
As compared to a paper notice, a plaque is made of more permanent material. Examples include:
- a brass tablet mounted on the exterior of a building to tell when it was constructed
- a tablet mounted on a monument to tell about an historic event
- a tablet given to someone to hang on the wall to acknowledge a bestowed honor
- a small piece of engraved metal mounted on a park bench to honor memory of them
(2) (plaque as in: dental plaque)
a sticky layer of germs and gunk that builds up on teeth
(3) (plaque as in: plaque in the arteries or brain)
a biological deposit that, in excess, can impede normal functioning