No idea, google comes up with physical vapour deposition, which seems closest. All I know is that on mine, there is no electrical continuity when using the two prong test.OK, but what does the abbreviation stand for?
If a switch faceplate was not metal, even though it looked like metal, then (a) it probably wouldn't have an earth terminal and (b) even if it did have an earth terminal(connected to what?) it would do no harm to earth it. In practice, I would imagine that the presence of an earth terminal, connected to the material of the faceplate, in a switch will virtually always mean that it is metal,and needs to be earthed.