Let me summarise, this is not a counterpoint but like to check if we are on the same footing before we go in circle again.
1. The tissue pack isn't identified, therefore, by strict interpretation of the law, it can be defined as un-possessed.
1.a. The tissue also therefore can't be treated like "S$1,000,000 cash envelope with your name/address written on it"
2. Cleaners, in the eyes of the law, is the same as public. Therefore whatever the cleaners have the right to do, so does the public.
2.a. The cleaners cannot make a judgment call if the tissue is under-possession or un-possessed, but a public can assume either way. And in your case, you can assume it as un-possessed, based on s/n 1.
3. The law is there and the judge interprets the law, no allowances if the law clearly spells out otherwise.
3.a. EPHA defines littering as any "(a) deposit, drop, place or throw any dust, dirt, paper, ash, carcase, refuse, box, barrel, bale or any other article or thing in any public place" therefore everyone is liable since everyone have, at one time or another, shed hair and skin in public place.
4. DPP will be the one to decide to prosecute or not
4.a. Hence, if a cleaner will not be prosecuted for throwing away a tissue paper used to reserve seats, a member of the public will not be either.