This week I started a test to signalize my availability with a traffic light. It's a small one I bought at Amazon which lets me change the color by pushing a button. Only disadvantage of this model is that the current color is always blinking (product description didn't say anything about blinking), but this should be enough for the test.
What the colors mean:
Red: I'm not available, please do not disturb!
Yellow: Only disturb me, if it's really, really important (like we're-all-gonna-die-important)!
Green: Say hello!
As soon as I have made some experiences, I will gladly share them here.