What do you call a device that tells a live audience what to do?

While reading this post on the Politics SE, I saw an answer that mentioned something which the poster referred to as a "crowd warmer:"

There are crowd warmers (*) that tell people when and how to cheer (clap after each sentence, cheer after the "highlight", cheer some more when politician talks about his opponent).

(*)I don't know the exact translation of the french term "Animateur de foule".

I tried looking up translations for the French phrase and had no joy. I looked up "crowd warmer," but it seems to mean "opening act."

I think I've seen something like an old-fashioned light-up sign that says "Applause" to tell live studio audiences to applaud, but the device I'm asking about could signal other actions as well. I've also seen supertitles at operas, but that's not the right word either. Is there a word or phrase for a modern device that does what the user described?

Example:

The ______ instructed the audience to cheer when the speaker raised both hands, but to boo when he shook his head.

Solution 1:

It is usually called "an applause sign".

When an "applause sign" begins to flash, it's time for the audience to clap hands and whistle and cheer. At least those who feel like doing it.