The guys at Wired In have launched a new product via KickStarter, a customizable bluetooth sign that can be activated either manually or via a number of triggers to politely let people know when you'd rather not be disturbed.
I could see myself using a sign like this in a number of instances. At our office, it's difficult to know whether a closed door means "Go Away" or if the door is just closed due to our noise office space. I've had to resort to the use of a post-it note on my door to let people know if I'm available or would rather not be disturbed. While it may get a few chuckles at first, this sign solves a lot of real world problems. I can also see a practice use for podcasters having an "On Air" sign to remind family members to keep the noise down.
The Kickstarter campaign has over 25 days to go and is just a few thousand dollars shy of their funding goal.