An identifier device, which may be part of a tracking or similar transponder device, which can be removably coupled to an article to be identified or tracked. Data representing the identity of the article is encoded in the form of a pattern, and can be read by the identifier device when correctly engaged to the article, by sampling the pattern so as to extract the data encoded therein for transmission. The pattern may be a relief pattern, for example in the form of bumps and pits such as a Braille pattern, or magnetic domains, or the like.