A marking liquid which contains a polymer dispersion with particles which are colored with marking agent, optionally further dyes and marking agents, one or more salts of a polyvalent, in particular bi- or trivalent cation, water and optionally moisture retaining agents and further usual additives, wherein the polymer forming the polymer particles is selected from the group of polyesters, polyester amides, polymers and copolymers based on acrylate or methacrylate with a proportion of free carboxylic acid groups of less than 10% by weight, melamine-formaldehyde-sulfonamide resins and mixtures thereof.