Or (the one that's so odd to me given most stations have trash cans) random drinks and the like above the urinals in lots of stations. Plenty of posters asking the dudes to please please please please please please please not leave trash there. Like I get wanting to get rid of evidence or something but they have trash cans right there!
I am not going to comment much on Singapore because I had not seen much random trash, I just really dislike cultural essentialism about cleanliness, because there's still clearly a good amount of people who are just totally not aligned with that. The cleanliness is a result of society doing things despite there being bad actors in the system!