A unique conductivity pattern is applied to printable articles to provide a "signature" for later verifying the authenticity of the printable articles. Preferably, the conductivity pattern is hidden from sight and differs from other conductivity patterns applied to other printable articles in an effectively random manner. Capacitive sensors read the conductivity patterns, and the resulting data for recording the signatures reflects not only details of the conductivity patterns themselves but also the characteristics of the capacitive sensors and their use.