In the office, where I am currently a temp. worker they have an interesting way of indicating whether or not the bathroom is available.

It's quite a small office and there is only one bathroom. So outside of it is a life size cardboard cut out of David Beckham with a sign hung around his neck. The sign says vacant on green background on one side and engaged on red background on the other. So when you proceed to the bathroom you flip the sign over. That way the whole office can just glance up and see whether or not the bathroom is occupied.

I can help but think: