That's my rule when a supervisor comes in, or at least, look like I'm not goofing off, I'm usually busy, just not always with work
Yea, the people at my job do it to an extreme.
I work in the college's security office helping out the locksmith, so I'm a bit separated from the rest of the office. However, I worked in there for a bit and see what goes on everyday.
There's one security officer who dispatches and sits at the front desk. There is another security officer, a secretary, and four student aides who do office work. The rest of the security guards go around and patrol.
For about half of the work day, the workers in the office either chat, watch movies, or just browse the internet. There's about one or two who are left to do the bulk of the work. The head of the office really doesn't care because he is swamped with other things to do. However, if his boss, the dean, caught what was happening, heads would be rolling. Luckily, the office is positioned at the end of a hallway on the side wall. So, in order to enter, you have to walk down a hallway and turn to your right, then have somebody allow you in. So, the guards monitor the camera for the hallway so they can see when people are coming to the desk, which cues them to look busy. They also listen for a loud clicking noise, because that's the dean with her high heals, which you can hear a mile away.