The invention relates to a method for marking a substrate with a unique library of nucleic acid sequence tags comprising: providing a library of nucleic acid sequence tags, comprising at least two different groups of nucleic acid sequence tags that each comprise a plurality of nucleic acid sequence tags, wherein each of said nucleic acid sequence tags comprises a defined nucleic acid motif in at least a first and a second characteristic position, and wherein outside of said at least two characteristic positions each nucleic acid sequence tag comprises a random nucleic acid sequence, wherein the combination of the nucleic acid motifs of the at least first characteristic position and the at least second characteristic position of a nucleic acid sequence tag is characteristic and unique for the group of said nucleic acid sequence tag, and marking the substrate with the unique nucleic acid library by applying the nucleic acid sequence tag library to the substrate. The invention further relates to a packaging article comprising a substrate marked according to the method of the present invention and different kits for applying and validating a substrate tagged according to the present invention.