While the number of signs you use when you begin teaching your infant sign language, ASL, or baby sign doesn't seem that important, it is. According to Signing Smart with Infants and Toddlers by Anthony and Lindert, the ideal number of signs to begin with is 6-12. When you use less then six, it takes longer for the child to understand that the movement means something and that it is a form of communication. Seeing a variety of signs throughout the day in a variety of contexts helps them understand and begin to sign sooner.
Interestingly, Anthony and Lindert have found that if you use more than 12 signs in the beginning, infants don't sign back as soon. According to Signing Smart,
Using too many signs initially will actually slow your child's signing back in that, instead of signing supplementing and highlighting English, it becomes a new code system to decipher in addition to English.Once your infant shows that he understands what the signs mean, or begins to sign back, add more signs to your vocabulary.