In this case face refers to "side". On information media that could be read on two sides (such as vinyl records or cassettes) the first was identified as 'A' and the second was 'B'. In the case of simple vinyls the main theme was on the 'A' side, and the 'B' had a fill song, so that face is associated with minor material. By extension, also the other side of something that looks good, and that in principle is not seen and can be your counterface. See b , a .
