I had the same issue when I was in an office and we were getting close to a deadline, so everyone was constantly chatting about this and that to unblock themselves. It's understandable when the rhythm of the office gets to that point that people want answers now, but it would get to ridiculous levels where you couldn't focus for 10 minutes before somebody else came by with a question.

I never got to the point of having a USB light as a semaphore or anything like that, but I really wanted to find and hack a toy traffic light that would indicate if it was a good time to interrupt me or not. So yeah, it was a very real problem.