The reason I sign to people 24/7 no matter who it is is because I "discovered" it while teaching ASL to a few people. One asked me why don't the deaf people sign because she works at a gas station and she had a deaf customer that "understood everything she said" and walked off while she was trying to inform him he left his keys. That was when she realized he was deaf.
So I took it upon myself to sign to people to see what results it would generate. It was surprisingly easy, and once you get over the hurdle of "signing to people" because its not in your comfort zone it will be much easier to live. That is how it is for me.
As of now, all the deaf people arent formally educated in that. They only have their social norm, upbringing, etc to go by. I am so grateful I learned to sign to people no matter who it is.
There is now a formal class in Gallaudet, and it's called Deafhood - it will cover this exact discussion, on top of many other issues.