Signing: To sign adult you start with your dominant hand fingers outstretched, palm facing down at shoulder height. Move your palm upwards until it is above your head.
The sign looks like you are illustrating the growth of a child into an adult.
Usage: You can use adult to refer to grownups. We often use contrast to help children understand the meaning of this word. For example, you can also teach the words baby, and child at the same time as adult to help you child learn what the words mean.
Flash Card: Click the link to view the Adult Baby Sign Language Flash Card. The flash cards are printable and available in both U.S. Letter and A4 sizes.