Disclosed is an item, for example a document, including a substrate having thereon a multiplicity of separate printed markings, wherein the printed markings include both conductive printed markings and substantially non-conductive printed markings. The different conductive and substantially non-conductive regions on the substrate can be detected, for example by measuring the resistance or current of each printed marking. The pattern of different conductive and substantially non-conductive regions can be used as a security pattern of authenticity that cannot be replicated by standard office equipment, and/or can be used to encrypt information in binary code form in the item. A system for forming and detecting the different printed markings is also described.