At eight food outlets, The Straits Times' campaign has also received positive results, with patrons and canteen workers making it a habit to remind one another to return trays.
Staff at the Institute of Mental Health have been rostered to encourage diners to return their trays at its canteen.
The Straits Times' Mop Squad - five reporters monitoring foodcourts - noted a general improvement in the overall cleanliness of the five Kopitiam outlets islandwide where the campaign started.
Cleaners are optimistic.
Said Madam Toh Li Ying, 60, who works at the Hougang Mall outlet: 'People are more considerate and have, at the very least, been putting all their utensils and rubbish inside the trays.'
This new awareness is the first step towards graciousness, said sociologist Paulin Straughan.
Youth, especially, respond to a sense of 'doing the right thing' - a 'hip' factor - to get them walking the talk. She said this set sees it as 'desirable to be seen as the 'in', educated and socially conscious group'.
Already, with the likes of the Facebook group, they are identifying with the cause.
Prof Straughan added: 'It's very encouraging that the younger, Internet-savvy crowd are championing social etiquette, and in doing so, investing in their social environment. If young professionals take on a lead role in advocating this social cause, it shows a lot of promise, as this is the group who will become the next set of leaders.'
Kopitiam's managers say diners have become more careful about how they eat - they now try to eat with their plates on their trays.
Its spokesman said it has been 'encouraging' to see diners clear their trays. The foodcourt chain is planning for more tray-clearing stations at soon-to-open outlets.
As most people will be in a rush, she said: 'We will work on strategically located clearing stations to make it more convenient for them to return their trays.'
Like environmental awareness, every bit counts.
Cleaner Cheong Kwee Ho, 68, who works at TIC Tech Centre, which houses one of the canteens that have adopted the cause, said: 'It's a gradual process, but I try to get them to clear their trays by reminding them as I walk past.'
Meanwhile, pupils at CHIJ Our Lady of Good Counsel, which adopted the initiative last week, are taking the practice of returning trays beyond their school.
Among them is Lim Jia En, eight, who said she has picked up the habit of clearing trays because 'this way, it's easier for other people to find a clean table and sit down'.
