To sign desert, first sign dry, then either make the hand signal for 'making a land area', or simply, 'area'.
To sign 'making a land area', bend both open hands and move them forward a short distance simultaneously. To sign 'area', take your dominant hand, form it into an open number 5 hand and make a circular motion with it, palm facing down.
Teach your baby or toddler the desert sign when you see a desert in their picture book or cartoon, or if you happen to be on a road trip and you are driving by a desert.
Teach your child this sign in context, as you see it in a book, on screen, or in person.