For a little while, it was a bit difficult to tell when Jonah had to potty. He hadn't really picked up on very many signs or verbal words yet, and he was moving so much that his usual cues got lost in all of his running around. Recently, I was relieved when I went to get Jonah up from nap, and he was standing in his crib, wiggling his fist back and forth in the air. Ah, the sign for "potty." At last! A definite cue to say "I need to go now!"
At first, Jonah used it after he had already gone. If I missed his other cues because I was upstairs doing the laundry, or I took a little longer to get him from bed, he would sign as if to say "I pooped Mom, and it's in my pants. Where were you?"
Then one day while we were visiting my mother and grandmother, he signed "potty." We were in the car, driving home from having dinner out. When we got home, I expected there to be a load in his pants, but they were only a little wet. Jonah was still signing "potty" but I thought he must just be signing it because I'm changing his diaper. I shrugged my shoulders and went out to the car to get a clean diaper. Yes, leaving him diaperless in my mother's care. When I opened the door, clean diaper in hand, I heard the most hysterical laughter. I looked at Jonah, who was still signing "potty" to my laughing mother while he was going. I cleaned the mess up, put a diaper on Jonah, and laughed myself. That is what you get when you don't listen to your child! From then on, he has signed "potty" before he poops. He still hasn't done the sign for pee yet, but he will make the "sssss" noise as he's going.
Here is the video of Jonah signing "potty" (excuse the laundry that snuck into the shot!)
Jonah Signs Potty (youtube link)