A plastic product such an animal ear tag (1) is laser marked with indicia (2). The contrast between the indicia (2) and the surrounding surface of the tag (1) is enhanced by the heated of the indicia following laser marking to a temperature at which the indicia and the surrounding surface have melted. In the preferred embodiment the indicia (2) is provided as a raised surface (3) and with a plurality of spaced apart peaks (4) with gaps (6) therebetween. The heating of the tag (1) is preferably by the application of a hot plate to the indicia surface of the tag and simultaneaouly or subsequently to the non-indicia surface of the tag.