It's not my term, though I wished I'd thought of it first. I think that Get Smart has gotten most of what I'd want to explain down. There are also generally other factors involved, (Get Smart already gave you the positive ones) Usually there is no visible, or some very obscure, branding, which is identifiable only by others in the know, so to speak. Often, the branding it is in plain view but generally not recognized, like the four stitches of a Margiela label, or the R or horse's head of R by 45RPM jeans. And in general, the pieces are plain, except for details that are appreciated only by other aficionados. The stitching on the back of Dior Homme jeans, for example. It can be a little obnoxious sometimes. It's like the club without a sign, which essentially tells the world "You are not cool enough to come in unless you are cool enough to have heard of this club."