Maybe they were just mute or deaf or both and were collecting for a charity that helps deaf and/or mute people.
Or maybe you just made that up to make your point :-|
There is no point. It was just a joke. Think about it - they don't believe in the existence of God, so their message about nothingness is silence.
OK, so it wasn't that good of a joke, but I thought it was... ;~)
(No ridicule of anyone's beliefs was intended.)