Abstract: A particulate coding material, e.g. for identifying the origin of a product by introducing it at source without its presence being readily apparent, comprises particles formed as thin transverse sections of an assembly of elongated elements, e.g. of plastic or natural fibres, of different colors and/or compositions forming a transversely united structure, e.g. having their longitudinal surfaces in adherent contact or contained in a matrix. The assembly can be produced by combining pre-existing filaments, e.g. by twisting, or by extrusion through a die, and may be drawn-down to a desired size (e.g. 10-150 .mu.m across) before sectioning. The resulting plurality of distinguishable areas in each particle (and, if desired, their relative locations) provide a coding facility. Larger flat bodies similarly formed, and the unsectioned elongated assemblies, also have identifying uses.