A few minutes after mating a kind of a waxy 'copulation plug' forms to prevent the sperm escaping. The plug is often expelled a few days after mating - you may find this in the bedding if you have attempted to breed with 2 of your pigs - a sure sign that mating has taken place - however sometimes this just dissolves so you wouldn't find it anyway. Signs of pregnancy include weight gain, the mother may start drinking more water, and you may be able to feel movement of the babies in the later stages (day 42).