[Pointman]

The weird thing to me is that you dont seem to have rules for such things. In Russia if your bag takes a seat, you have to buy a separate ticket for it. Although I have only seen it a couple of times in my life, you can buy two tickets and occupy two seats - one for you and another one for your bag. If you only have one ticket, driver or ticketman can order you to remove the bag from the seat - although I have never seen it happened because noone does it at the first place. There's no grey area, no etiquette or something. It is pretty straightforward, you either paid for your bag or not. Kinda surprise you do not have simple and effective rules for that.