[EvertonDiehard]

🤢 'Smell intensifies when it's hot': Chinatown TCM shop hit by bags of urine, trash from HDB block
Even passers-by sitting at the nearby pavilion have not been spared from being splashed with urine, said Tay, adding that the smell of the human waste "intensifies when [the weather is] hot".

I suspect that it is the work of low SES seniors too weak or lazy to go to the bathroom to ease themselves. They get rid of their waste by flinging these plastic bags out of their windows.