At a previous employer, we played "donuts". If you walked away from your station and didn't lock it, then whoever noticed this would pop up a new email and send it to the "Admin" group address with the word "donuts" as the subject (which takes all of about 10 seconds). Who ever was dumb enough to leave their station unlocked then had to buy donuts for the entire admin team that Friday. It was a fairly large admin team, so you had to be ready to shell out 50-60 bucks.

A little goofy, but it drove the point home...lock your station every time, or it will cost you.