None is signed by touching your thumbs to your fingertips to make the ASL letter 'O' shape with each hand. Then starting with your arms crossed, break them apart. The motion looks like you saying there is nothing there.
As your baby's counting gets more advanced, you can add the concept of none. Start with one, two, and many. Then add none.
Teach the sign for none in the context of other numbers concepts, such as one, two, and many.
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