a process for producing markings or lines engraved on a sheet or a tubular piece made of plastic material or multi - layered metal - plastic material less than 1 mm in thickness , in which the sheet or piece is gripped between a tool bearing one or more marking contour and a resilient support , in order to produce the engraved markings or lines . the sheet or piece is at less than 50 ° c . during the gripping stage , and in the resilient support has a shore hardness d of between 70 and 120 , the markings or lines obtained being produced by plastic deformation with elastic return .