✔ 最佳答案
It does not have to be MTR Bylaw (Hong Kong Ordinance Chapter 556B).
For such action, the person can be prosecuted by:
- Disorder in public places (Hong Kong Ordinance Chapter 245 "Public Order Ordinance" Section 17B):
http://www.hklii.hk/chi/hk/legis/ord/245/s17b.html
and/or
- Prohibition on display of indecent matter (Hong Kong Ordinance Chapter 390 "Control of Obscene and Indecent Articles Ordinance" Section 23):
http://www.hklii.hk/chi/hk/legis/ord/390/s23.html