What the hell is an etiquette bell?

Sorry folks, maybe I am not so cultured, maybe I don't know much about etiquette but really what the hell is an Etiquette Bell?? I never figured it out. Having been to Japan a couple of times..I never figured out what this is and frankly I never bother to asked either.

Btw....this is found in their toilets!

So, my hypothesis - the bell is for :-

1) If my shit stinks - I should ring the bell.....

2) If I need help to get out of the toilet...I should ring the bell.....

3) To distract the noise of peeing and shitting by continously ringing the bell....

I admit, I am ignorant....just tell me if you know what it is for......