Back in my day the arrogant devs just used printer paper and a hand drawn sign saying "GO AWAY!" taped to the back of their chair.
In my tribes, the universal "please don't bother me right now" sign has more typically been the wearing of over-the-ear headphones.
I wish I had the same tribes as you. People always come up to me when I'm wearing my headphones, even trying to get my attention in public