This couple that was in the same train as me, left their seats to change the diaper of their little baby.
Not only did they go away from their luggage, but they left two phones and a large tablet visible and unattended for quite some time!
It's funny how even in countries where people leave their expensive belongings unattended without worrying still sees bikes as acceptable targets as if it's like a global standard. I would also put umbrellas there too.