A method for forming a hidden tear seam (14) in the cover (12) for a safety air bag assembly includes the steps of filling a heated open mold with liquid plastisol or dry powder composed of polyvinyl materials; forming a gel layer of polyvinyl chloride material on an open heated thin metal mold; dumping excess polyvinyl chloride plastisol material from the gel layer; fusing the gel layer; stamping a tear seam (14) in a fused layer while it is still plastic by providing an anvil having a surface thereon of a first predetermined area and including an embossment thereon extending outwardly of the first predetermined area and stamping the tear seam (14) by directing the embossment into the fused layer until the surface engages the fused layer and wherein the first predetermined area is sized to produce a reaction force on the anvil to determine the depth of penetration of the embossment and thereafter finally curing and cooling the fused layer and removing the layer from the thin metal mold.