An apparatus is provided for magnetically imprinting indicia into a layer on an article, the layer comprising a composition in which magnetic or magnetizable particles are suspended. The apparatus comprises: a soft magnetizable sheet, having an outer surface arranged to face the article in use, and an opposing interior surface; and a permanent magnet, shaped such that its magnetic field contains perturbations giving rise to indicia. The permanent magnet is disposed adjacent the interior surface of the soft magnetizable sheet. The soft magnetizable sheet enhances the perturbations of the magnetic field of the permanent magnet such that when the layer to be imprinted is located adjacent the outer surface of the soft magnetizable sheet, the magnetic or magnetizable particles are oriented by the magnetic field to display the indicia.