And this is what it looks like when 90.000 people hold up their mobile phone as requested by the men, Mr Bono himself.
But I thought I'd share this little anecdote with you.
U2 were playing at a concert in Glasgow in 2006, when Bono asked the audience for total silence. Then in the silence, he started to slowly clap his hands, once every few seconds. Holding the audience in total silence, he said into the microphone,
"Every time I clap my hands, a child in Africa dies."
A voice from near the front of the crowd pierced the silence...
"Well, f***ing stop doing it then!"
OK sadly this is only a rumor but it did made me laugh when I heard it for the first time so I had to share it.