Moon is a great sign to do on a cloudless night. When your baby's attention is drawn to the moon, say the word, and when they look at you, do the sign. If you want to direct their attention to the moon, draw their attention by saying the word, then make the sign and point to the moon.
You can use height when you present the moon sign, to help your baby learn that the moon is up in the sky. Hold the moon sign flash card up higher than other flash cards.