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!
One lady saw me locking my bike up with 12mm thick chain and expressed sadness that we have to go to such lengths as a society just to keep others from touching things that aren't theirs. I sometimes think of her now when I'm locking up my bike.
Doubly sad too, since some people don't have cars, and bikes are their primary means of transit.