Shut up; the impossible task for some people in theater (an on buses)

I mean ..Come on! Don’t you notice that people are listening to you (unwillingly)?

I, like most people, can control myself not to say anything to alert the people who talk so loud in such places to shut up.

But what I’m concerned is that I’m afraid for them. I’m afraid that someone will eventually take some hard action and consequently lead the situation into worst.

The weather is getting hot and people tend to get mad easily.

So, I don’t know what to do. I just wish that there’s an alarm sign in every seat in theater and on buses that can alert people (with a furious, red, blinking light) when they are being an unnecessary broadcaster.