A polite note was also seen left on a vandalised police van, apologising for the damage.
The unpopular Beijing backed leader of Hong Kong, Chief Executive Leung Chun-ying, has urged people to leave the protests, which were declared "illegal" by China.
"We don't want Hong Kong to be messy," he said in a statement broadcast on Monday.
Attempting to dispel rumours of intervention by the Chinese army, he added: "I hope the public will keep calm. Don't be misled by the rumours. Police will strive to maintain social order, including ensuring smooth traffic and ensuring the public safety."
One of the key demands of the occupation is his immediate resignation, along with proper consultation on political reform to allow free and fair elections in Hong Kong with universal suffrage.
On Twitter, one supporter of the movement wrote: "Hong Kong: A city where protestors don't smash up shops, and they also clean up after themselves, yet get teargassed and pushed by the police."
Many volunteers were wearing the yellow ribbons symbolising support for democratic reform that have started appearing on street signs and at entrances to underground stations.
The movement, dubbed the Umbrella Revolution because of the widespread use of umbrellas against tear gas and pepper spray, has sparked solidarity protests around the world.
Demonstrations are being run by a group called Occupy Central with Love and Peace, which describes itself as a "non-violent direct action movement that demands a fully democratic government in Hong Kong".
- UK Independent