Why is there a pentagram on the lid of some plastic containers?

depending on what it is you are reffering to, I imagine it would be either the pressure safety seam, which causes the lid to split open before the contents reach a pressure great enough to burst the container, or otherwise a quality control design, that allows the lid to remain flexible by providing a joint. as to why it's shaped like a pentagon... it's a simple geometric shape, and maybe someone didn't like the fact they had to add them to their products and thus made a subtle jab at the regulation.