This is the sign for dress, as in putting on clothing (not the item of clothing). To sign dress, take both hands with fingers spread, and move the hands down the front of your chest to your waist area, leading with your thumbs. The sign for dress looks a lot like you are showing off your fine Sunday dress.
When your baby is learning to sign, you are probably dressing them. Signing dress before you change them prepares them and will reduce fussiness, as the baby knows what to expect. As your baby gets older and can start to put on some of the easier items of clothing, you can use the sign to signal that it is time for them to dress themselves.
The sign for dress is most suitable for little girls. We like to teach it by letting our little girls pick their favorite dresses. Dresses are also a good opportunity to practice colors.