A vector graphics file includes at least one artwork layer and at least one watermark layer. The watermark layer comprises a pattern of vector graphics primitives, each of which is filled with a color that is a tinted variant of the color of the location in the artwork that the primitive overlies. Such layered arrangement enables the watermark to be added or omitted, and varied in strength, payload and appearance, at will. Yet the artwork is left unchanged through such manipulations. In some embodiments the watermark conveys a multi-symbol Global Trade Item Number (GTIN), and the file is used to generate a label or packaging for a food or general merchandise retail item. A great number of other arrangements, features and advantages are also detailed.