On Orchard Road, a group of several volunteers from the Cat Welfare Society stand and observe as an officer from the National Environment Agency (NEA) confronts a litterbug.
They watch as he asks the offender, politely but firmly, to pick up and bin the litter properly.
"We were taught to be non-confrontational and polite. The whole concept is just to persuade them not to litter," said volunteer Phyllis Tan, 36.
This is part of a new NEA training programme to empower volunteers in several non-governmental organisations to curtail littering offences.
Some 60 trained volunteers will be issued accreditation cards in the next few weeks, which give them the authority to ask litterbugs to bin their trash.
And if they refuse, to take down their particulars.
Volunteers are not aware of the exact date they will receive the cards. For a start, the volunteers will come from groups such as the Public Hygiene Council, Waterways Watch Society, Singapore Kindness Movement, Singapore Environment Council and the Cat Welfare Society.
The idea to include members of the public in the effort to prevent littering was first floated by Minister for the Environment and Water Resources Vivian Balakrishnan to NEA last year.
He said then: "We believe that, in fact, we need to reclaim community ownership and community action (over the environment)."
Then-NEA chief executive Andrew Tan said at the time: "We need to get to the very heart of behaviour change by promoting the right social values, including 'zero tolerance' towards litter."
The number of littering offences went down from 41,392 in 2009 to 11,131 in 2011.
But chairman of the Public Hygiene Council, Mr Liak Teng Lit, has said that littering remains a serious issue, and that some Singaporeans litter "with impunity".
Trained volunteers will not go on patrols, but are encouraged to dissuade people when they witness them littering.
Over two half-day sessions last month, volunteers also engaged in role-play.
They also learnt to "walk away" if an encounter with a litterbug turned aggressive, said Ms Tan, who acknowledged the risk of conflict. "I mean, if I'm a litterbug and somebody approached me, I would also ask: 'Who are you?'"
She added: "And if we approach litterbugs and they refuse to pick up their litter, what are the chances that they will give us their particulars?"
Should difficult situations arise, volunteers are advised to seek help from NEA officials or note down the particulars of the offender.
Some commentators expressed scepticism.
Sociologist Daniel Goh of the National University of Singapore said: "Ethically, I don't think it is right for a government agency to pit citizens against citizens and expose people to potential violence."
Associate Professor Goh suggested nudge tactics such as creative campaigns and surveillance cameras to change littering behaviour.
But some believe that the task of keeping Singapore clean should not be left only to the authorities. Getting volunteers to come on board is a good ground-up approach.
Said Dr William Wan, general secretary of the Singapore Kindness Movement: "It is important to have a critical mass to create social pressure."