A product 2 has a data encoding pattern 6 thereon. The pattern comprising a plurality of pattern cells 200 each of which has a pattern selected from a group of cell patterns. Each cell pattern comprises a plurality of cell elements 204 each of which can have any of a plurality of marking states, such that the marking states of the elements produce the cell pattern. Each cell pattern has at least two lines of symmetry. At least some of the cells are arranged in a manner which is dependent on the position of the content
