How do I know if the milk seal has been broken?

Tamper evidence on our milk products is provided by the blue cap being attached to the base of the pouring fitment by 2 breakable "legs". These are broken when the pack is opened. The twist action of the cap rotates a cutting ring located in the pouring fitment which in turn cuts the foil seal and pushes it out of the way of the flow of product, hence the fact that you do not see a foil seal when the cap is removed. If the pack is opened and re-sealed, these "legs" on the caps will not line up again. If the cap is made to line up so that it looks like the seal is not broken, the pack will leak if inverted, and inevitably will spill product if the pack is picked up and squeezed.