You're right about that, Martin. It may not even be a perceptible nod. Sometimes with my group, it's just a smile, or a slight movement. That comes from playing and singing with other musicians for a long time, until communication becomes intuitive.

In the meantime, a not works fine.

Just a humorous aside... I asked the bass singer in my group to count out the beat before he started to sing on a song where we all try to start out on the same note, and we do it a capella. He agreed that that was a good idea, and we went to sing the song again, he suddenly started singing. I told him that he was supposed to count out the beat before he started singing, and he said, "I did." We all burst out laughing, and I said, "You can't just count it out in your head! You've either got to count it out softly so that we can hear it, or give us the beat with your hand."

Jerry