Some blame the tourists, especially the young 20-something "Easyjet set" who ride the budget airline to party through the night in the uber-cool, hedonistic German capital, for a host of ills from rising rents to noise pollution.

"Noisy tourists go home!" reads one hostile sign in the eastern district of Friedrichshain. "Berlin doesn't love you," say stickers plastering traffic lights in nearby Kreuzberg.

A gallery in an area known for its trendy bars featured for months a scrawled sign in the window: "Sorry, no entry for hipsters from the U.S."

"We've seen people insulted for looking like tourists or get disparaging looks," said David Schuster, an activist for a local leftist group that has launched a tourist-friendly awareness drive.

"There's some resentment that tourists party loudly or throw up on the streets," Schuster said. "I think many Berliners do too, but they feel entitled to act that way."

Berlin, now Europe's third most visited city after the more established magnets London and Paris, can ill afford to scare away the tourists.

Tourism generated gross revenues of 10.3 billion euros last year, equal to nearly 10 percent of the city budget, a recent study by the Berlin government said. That is more than either real estate or consumer goods production, two other expanding branches of Berlin's otherwise plodding economy, it showed.

Nine new hotels are set to open by 2013.

Yet this summer, visiting investors at a business convention were attacked by some hundred demonstrators and a newly opened "organic hotel" was vandalised by anti-gentrification activists.

These protests represent those of a small minority, said Burkhardt Kieker, director of VisitBerlin, the city's main tourist service agency.

"Berlin is regaining the status of a world city. We are becoming a mass tour destination. The average Berliner is honoured by the tourists," he said.

"Paris and London have had hundreds of years to get used to their many visitors. We've only had 20 so far," he said, referring to the fall of the Berlin Wall in 1991.

The fall led to the reunification of Germany, the reinstatement of Berlin as the German capital and some glittering restorations, which have made the city an attractive destination for tourists. (Editing by Paul Casciato)

• A Permanent Economic Emergency