Spencer Clark explains why everyone needs to be "deaf aware", the different types of deafness, how deaf people might be different, methods of communication and how there is no one solution for all. Hop over and take a peek at what he wrote, or, better yet, print it out, post it at your place of work where you and your employees can see it. Be sure to forward "How to Recognise a Deaf Customer" to everyone you know.
This really should be posted at every work station.
Be sure to also check out Spencer's website at DeafWise