An identifiable mark on a portion of a polished facet of a surface of an article and being identifiable by an optical magnifying viewing device, said identifiable mark comprising: a nano-structure formed by a two- dimensional or a three-dimensional lattice of a plurality of discrete nanometer sized recessed or protruded entities, wherein said entities are arranged within a predefined region of said polished facet in a predetermined arrangement in relation to each other, and such that an outer interface surface between the facet of the article and air is formed and an inner interface surface between the facet of the article and air is formed; wherein said predetermined arrangement of said entities is a non-uniform and non-periodic arrangement, and wherein said entities are sized and shaped so as to cause optical scattering upon reflection of incident light, and the distance from the inner interface surface to the outer interface surface is greater than the amplitude of the non-marked portion of said polished facet; such that upon reflection of incident light, said incident light having one or more predetermined wavelengths by said lattice at a predetermined angle of incidence to said lattice, interference due to scattering of light from said lattice is induced, such that reflected light has a variation in intensity providing one or more local maxima of one or more wavelengths; and said mark is invisible to the naked eye and is invisible when utilizing a typical camera equipped microscope under normal light conditions and said mark is identifiable by way of an optical magnifying viewing device inclined at a requisite viewing angle and upon light of one of more wavelengths being scattered from the lattice of the mark such that a local maxima is detected and the mark is identifiable by one or more colours of said one or more wavelengths. a nano-structure formed by a two- dimensional or a three-dimensional lattice of a plurality of discrete nanometer sized recessed or protruded entities, wherein said entities are arranged within a predefined region of said polished facet in a predetermined arrangement in relation to each other, and such that an outer interface surface between the facet of the article and air is formed and an inner interface surface between the facet of the article and air is formed; wherein said predetermined arrangement of said entities is a non-uniform and non-periodic arrangement, and wherein said entities are sized and shaped so as to cause optical scattering upon reflection of incident light, and the distance from the inner interface surface to the outer interface surface is greater than the amplitude of the non-marked portion of said polished facet; such that upon reflection of incident light, said incident light having one or more predetermined wavelengths by said lattice at a predetermined angle of incidence to said lattice, interference due to scattering of light from said lattice is induced, such that reflected light has a variation in intensity providing one or more local maxima of one or more wavelengths; and said mark is invisible to the naked eye and is invisible when utilizing a typical camera equipped microscope under normal light conditions and said mark is identifiable by way of an optical magnifying viewing device inclined at a requisite viewing angle and upon light of one of more wavelengths being scattered from the lattice of the mark such that a local maxima is detected and the mark is identifiable by one or more colours of said one or more wavelengths.