Abstract: The invention relates to the labelling of textile and other flexible sheet articles in which a marking element is used which is adapted to be attached and bonded to the article by heat and pressure, said element including a heat-curing film-forming resin system in the presence of blocked cross-linking groups and under acid conditions, such resin system becoming heat-cured during the attachment of the marking element to the article to form an inert, insoluble and wear-resistant marking on the surface of the article. The resin system may be an alcohol-soluble copolyamide in the presence of a cross-linking agent which may be a precondensed alcohol-modified formaldehyde or aminoplast resin containing alkoxy alkyl group; or it may be a dispersion of a film-forming addition resin system at least one monomer of which contains groups capable of reacting with similar cross-linking agents or comonomers bearing alkoxy-alkyl groups.