Charles Spurgeon Commentary Luke 1:21-22

"And the people were waiting for Zacharias, and they marvelled while he tarried in the temple. And when he came out, he could not speak unto them: and they perceived that he had seen a vision in the temple: and he continued making signs unto them, and remained dumb." — Luke 1:21-22 (ASV)

By the signs he made, he impressed them with the fact that something extraordinary had happened.