Signing: Many is signed, by showing your many fingers. Start with your fingers made into a fist, then open them up spreading out your fingers.
Usage: When your child is young, their ability to count will often be limited. So instead, we use the signs for one (when there is a single object) and many (for any larger amount).
Flash Card: Click the link to view the Many Baby Sign Language Flash Card. The flash cards are printable and available in both U.S. Letter and A4 sizes.