To sign bill, hold your non-dominant hand open and horizontally before you, palm facing in and thumb sticking up. Then take your dominant hand and use it to grasp your non-dominant hand, starting from the curve at the base of the thumb and sliding to the edge of the index finger. It is like you are tracing the top edge of a dollar bill.
Teach your child the bill sign in the context of handling money when organizer your billfold at home, or when you are buying something at a store or shop. Eventually, there will be a good opportunity to start your kids young and already make them aware of the value of money, saving for a rainy day, and making mindful purchases.
This is a useful flash card taught best in conjunction with actual purchases, or when your toddler sees play money at home.