Sign busy by taking your non-dominant hand and laying it horizontally in front of your body. Then take your dominant hand, palm facing forward, and move it in a horizontal motion, left to right and back. An alternative ASL sign for busy uses the letter B hand instead of a flat, open palm.
The sign looks a little like your are blocking someone's path with a stop sign - because you are too busy.
Use the busy sign to let your baby know when your attention is elsewhere and they need to wait a little before they get your full attention.
Busy is a great sign to teach patience in older children. Having your baby learn that sometimes they need to wait patiently for a few minutes to get what they want will help them develop self-control and also independence, as they will often just do it themselves rather than wait for you.