To sign husband, take your dominant hand and form the general 'male' sign at your forehead (an open, curved hand that looks like a modified 'C'). Then take that hand down to hold the upturned non-dominant hand, also forming an open curved or modified 'C' sign, but with your palm facing up). This mimics the hand-holding of husband and wife.
Teach your toddler the husband sign when you are explaining the relationship of Daddy to Mommy, or Grandpa to Grandma, Uncle to Aunt, and so on.
This is a useful flash card taught best in conjunction with the other family flash cards.