In the past, I've had reports to me that soiled nappies were put in the seat pockets. I did make a PA one one flight that if any human waste was put in the seat pockets, the passenger occupying that seat would receive the cleaning bill. That did result in two letters of complaint, a round of applause from the cabin crew and SOME of the other pax as well. Quite frankly, I have no time for people who act like pigs, but I have all the time in the world for considerate customers that I would want to fly again.