My coment is not at all talking about what the OP was doing. I think that he went beyond what he ought to have. I am specifically referring to the mentality of "employees should trust their coworkers and can therefore leave their computers unlocked".
I didn't say they have to keep their computer unlocked, some of them did lock, but I did not enforce a locking policy because I don't think it was necessary in the context. And if I did have to enforce screen locking in other places, it would be out of question to use any passive aggressive behavior or public shaming towards a teammate, if you need trust from your employees, you treat them well. My first reflex would be to look at technology, because locking the computer is a stupid and consistent task and technology is for stupid consistent things.
I think people are too focused on working for military and paranoïa, we need a range of behaviors, from the paranoid to the welcoming, that guy watching your screen could start an interesting discussion about your project, and give you the contact to the right person to help you. You don't want that in a military context, you highly desire it when you're building a vegan pet food marketplace for hipsters.
Not everyone needs to develop like in Aerospace, not everyone needs to develop like in video games, not everyone needs de behave like a NSA agent, and not everyone needs to behave like a farmer's market salesman, we need a range of behaviors.
And whatever the policy, you never, ever, let co-workers be dicks to each others, no "pranks", no public shaming, no sending a prank email from each other's computer. If security is really an big issue, then not locking a computer is a strike, it goes between the boss, the offender and HR, not a matter of joke.
