The present invention relates to the use of non deactivable security markers comprising the combination of at least two types of nanoparticles of materials presenting Raman effect, wherein said nanoparticles are in a dispersed state or is forming agglomerates of between 2 and 500 nanoparticles. The invention also relates to security documents, articles or elements incorporating these markers, as well as to a method and system for the detection thereof.