This is baby-talk for "more, please!" Within 24 hours of learning the sign for please, Luke began to say it as well. It's super cute to see and hear him ask for more food, playing, tickles, or anything at all, especially when he does so with such nice manners! Not bad for 16 months. I'm impressed.
For anyone thinking about using baby sign language, I would highly recommend it. It's a lot of payoff, for not a lot of work. I learned about 20 or 30 signs myself, and began integrating them as they seemed to fit into our lives. So easy, really!