Teaching more complex emotion signs - like angry - is for more advanced babies. It is a useful sign, because it helps you identify and acknowledge an emotion that a child is feeling. While this will not in and of itself defuse a tantrum, it can help reduce the frustration at not being understood that usually causes these tantrums in toddlers. Angry can be taught using books, watching cartoons, and also just by pantomiming the emotion when you are teaching the sign. Teaching an opposite emotion like happy as a contrast also helps some children catch on to the meaning of the word.
The sign for angry is best learned during the toddler stage, when your child is likely to struggle with expressing emotions. Teach the sign contextually, and once your toddler grasps the type of emotion that the sign for angry represents, introduce them to the flash card to provide visual feedback.