Breakfast is a combination sign of both eat (food) and morning -- and whichever sign you make first doesn't really matter as long as your baby understands them in tandem.
Eat (Food) is signed by taking your dominant hand with thumb touching your four fingers, then bringing the hand to the mouth repeatedly. The sign for morning looks like the sun rising over the horizon. First, take your non-dominant hand and lay it horizontally to make the horizon, then bring your dominant hand under and over, hinging at the elbow to make the sun rise up over the horizon.
Usage: Breakfast and other meal-specific signs like lunch, dinner, and snack, are good advanced signs to teach once your baby has mastered the basic eat sign. Adding a time-of-the-day dimension adds a little to the difficulty and keeps your baby challenged.
Breakfast is a big deal in our home. In fact, some of our kids learned to sign breakfast before learning how to sign any other meals. To encourage the use of this sign, ask your baby about their favorite breakfast foods.