To sign thin, your non-dominant hand creates a flat surface with palm facing upward. Your dominant hand travels from the wrist to the tip of your non-dominant hand, with index finger and thumb almost meeting together, indicating that something is "thin". Also, shrug your shoulders forward to emphasize the idea of a thin person.
We use thin to equip our babies to better describe objects and people.
Use the thin flash card when you are beginning to teach your baby about contrasts in shapes and sizes.