An aqueous dispersion of polymers which have a particle diameter of at least 1 μm and comprise a fluorescent dye, wherein said dispersion is obtainable by free radical suspension polymerization of ethylenically unsaturated monomers in an oil-in-water emulsion whose disperse phase comprises at least one fluorescent dye dissolved in at least one ethylenically unsaturated monomer and has an average particle diameter of at least 1 μm, in the presence of at least one surface-active compound and at least 0.5% by weight, based on the monomers, of at least one hydrophobic, nonpolymerizable, organic compound, of a hydrophobic polymer of at least one C2 to C6-olefin having a molar mass Mw of up to 10 000, of a siloxane having a molar mass Mw of up to 5000 and/or polystyrene having a molar mass Mw of up to 10 000.