The invention relates to 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.