How many will show up, let alone stay to camp out to disrupt city centers for days, or months, to come, is anyone's guess. The hundreds at Manhattan's Zuccotti Park were calling for back-up on Friday, fearing imminent eviction. Rome expects tens of thousands at a national protest of more traditional stamp.

Few other police forces expect more than a few thousand to turn out on the day for what is billed as an exercise in social media-spread, Arab Spring-inspired, grassroots democracy with an emphasis on peaceful, homespun debate, as seen among Madrid's "indignados" in June or at the current Wall Street park sit-in.

Blogs and Facebook pages devoted to "October 15" - #O15 on Twitter - abound with exhortations to keep the peace, bring an open mind, a sleeping bag, food and warm clothing; in Britain, "Occupy London Stock Exchange" is at pains to stress it does not plan to actually, well, occupy the stock exchange.

That may turn off those with a taste for the kind of anarchic violence seen in London in August, at anti-capitalism protests of the past decade and at some rallies against spending cuts in Europe this year. But, as Karlin Younger of consultancy Control Risks said: "When there's a protest by an organization that's very grassroots, you can't be sure who will show up."

Concrete demands are few from those who proclaim "We are the 99 percent," other than a general sense that the other 1 percent - the "greedy and corrupt" rich, and especially banks - should pay more, and that elected governments are not listening.

"It's time for us to unite; it's time for them to listen; people of the world, rise up!" proclaims the Web site United for #GlobalChange. "We are not goods in the hands of politicians and bankers who do not represent us ... We will peacefully demonstrate, talk and organize until we make it happen."

By doing so peacefully, many hope for a wider political impact, by amplifying the chord their ideas strike with millions of voters in wealthy countries who feel ever more squeezed by the global financial crisis while the rich seem to get richer.

"ENOUGH IS ENOUGH"

"We have people from all walks of life joining us every day," said Spyro, one of those behind a Facebook page in London which has grown to have some 12,000 followers in a few weeks, enthused by Occupy Wall Street. Some 5,000 have posted that they will turn out, though even some activists expect fewer will.

Spyro, a 28-year-old graduate who has a well-paid job and did not want his family name published, summed up the main target of the global protests as "the financial system."