Before my daughter could talk, we taught her some basic baby sign language. Well, truthfully, we only taught her "all done." When she was done with her food, she would hold both hands up and twist them at the wrists, doing a sort of double-wave.
At first, it was great. We could finally understand when she was done with her food. It took a lot of the guesswork out—is she done yet? is she still hungry? But it wasn't long before she was seemingly saying "all done" just about before she started.
A new problem was created. Now we were concerned about her eating enough. It felt mean to force feed her, but we wanted her to eat enough. What do you do if your preschooler isn't eating enough?