Venice is stepping up a campaign against badly behaved tourists in an effort to reduce friction between its residents and the 20 million people who visit the city each year.

Having declared war on the pigeons which have become synonymous with St Mark’s Square, the city has launched a fresh set of initiatives to try to keep the ravages of mass tourism at bay. Large posters asking visitors to Tenere La Citta Pulita (Keep the City Clean) are to be posted in prominent spots, the city’s “clean-up tsar”, Augusto Salvadori, announced this week.

Shocked by the often boorish behaviour of tourists, Venetians are reminding visitors using vaporetti (water buses) to give up their seats for elderly people and pregnant women, and urging backpackers to remove their unwieldy rucksacks before boarding.

Foreign fare dodgers will also be targeted, said Mr Salvadori, who as councillor for tourism has been charged with improving “public decorum” in Venice. “The fight against fare dodgers will be unrelenting,” he said. “You won’t be able to board without showing your ticket, and we’re studying the possibility of installing turnstiles.”

The moves are the latest phase of a campaign started in 2006 to spruce up the city’s image and clamp down on unacceptable tourist behaviour. A group of young women called City Angels aims to stop visitors dangling their feet in fountains, walking around shirtless and throwing food wrappers on the ground.

“They wander about without their T-shirts on as if they’re on the beach, rather than in a historic city,” said a city official who asked not to be named. “Tourism has a huge impact on Venice – there are 60,000 inhabitants but 20 million tourists. It’s a matter of trying to get along together.”

Venice authorities also want to deter people from lowering the tone by eating fast food and packed lunches in popular locations such as St Mark’s Square.

Mr Salvadori has scored a number of successes since the city launched its crusade against bad manners, litterbugs and uncouth conduct. A ban on street vendors selling grain has led to a significant decrease in the estimated 20,000 pigeons in St Mark’s Square. The birds’ acidic droppings threaten Venice’s exquisite Renaissance palazzi, fountains and statues.