[tomtoise]

I worked somewhere where the behaviour described in OP's post happened. It was just lighthearted. We worked in desk 'bays', so someone sat next to the unlocked PC would have visuals on what the prankster was doing on the machine. Harmless emails like 'I'm buying the whole office donuts at lunch' were sent. It was very rare for any employee to leave their machines unlocked twice with this unofficial procedure in place.