When a pig is rubbing it's nose on you it means that the pig is showing affection towards you and basically letting you know it loves you.
As a kid I used to have a little baby pig that would hold sometimes and the pig would rub it's nose on my nose at times and I could tell that he loved me.
Most pigs don't like to be held but the piglet I had loved being held so it can depend on certain pigs but when they're rubbing their noses on you then you can usually be sure that they love you or they're wanting your attention.