The invention concerns a method for marking a feature substance, present in particular in pulverized form, with at least one marker, with the feature substance being suitable for the authentication of value documents, comprising the step of mixing the feature substance with a small quantity of the marker present in the form of particles, so that the macroscopic detectability of the feature substance is not influenced by the marker and the marker is detectable in a value document having a security feature containing the marked feature substance by means of a spatially resolving analytical method which is adapted to resolve down to the single-particle level.