|Thanks for not horking...|
"Spitting spreads germs" it says with a HK$5,000 ($643) fine if you're caught.
The transportation company probably had to put up more of these signs around its stations due to the increased number of passengers visiting from the mainland.
Perhaps while it's educating our northern cousins about social etiquette it could also add another sign asking people not to crouch?
It only makes their provenance even more obvious...