Sit in Baby Sign Language looks like a person sitting on a ledge. Start by holding your non-dominant hand horizontally, with index and middle fingers extended to make the ledge. Take your dominant hand with index and middle fingers extended together in a slight hook to make the person's legs, and sit them on the ledge.
Sit is a good sign for older toddlers that are ready to learn more control. Sit is a good way to calm down their state.
You can take a child from running around to sitting using the sign, and that will help them mentally transition to another activity like eating or drawing.