That's a good point. They rarely shout about things like stamp collecting, or about how the end isn't nigh, or about how you're probably not going to Hell.
Toronto's two famously startling denizens of the street for the longest time was a guy known for scaring the crap out of tourists at Yonge and Dundas by suddenly shouting BELIEVE!!! followed by end-of-time messages, and this short tiny old man who always dressed in brown, who would randomly stop, turn around quickly, and start swearing profusely. The reactions from people unlucky enough to be behind him were often golden moments to behold.
You can find dozens of videos of them on Youtube. I'm sure every city has their versions of these two near-celebrities, and I'd be a little disappointed if they don't.