To sign worm, create a wall with your non-dominant hand in front of you. Then with your dominant hand, stick out your pointer finger and move it horizontally against the "wall" of the other hand, mimicking a worm that is crawling through the dirt.
Use the worm flash card when conducting outdoor discovery trips. We also use it when learning songs and rhymes.
Teach your baby the worm sign in context, whether she encounters this via picture books, TV, or in your garden. Introduce worm along with the other signs for bugs and animals, both domestic and wild.