Our first step in learning to sign for Dizzy was to go out and buy a pocket dictionary of signing (for more information on ASL - American Sign Language click here). We used the dictionary to give us guidance on the types of sign to use and it proved to be very useful, but over time we found that our own signs were sometimes more effective because when signing for a dog the signs need to be VERY clear.
For example originally we used the sign for the word 'no' (bringing the right thumb, index and middle fingers together) when dizzy was doing something undesirable, but we found that this was a little to subtle for her and she didn't seem to understand. So now we waggle a pointed index finger vigorously at her accompanied with a big frown and a shake of the head, and she will almost always stop what she is doing.
Facial expressions seemed to help a great deal in helping Dizzy to understand signs, so where possible we always ensured that she could see our faces clearly. Actually saying the command out loud also helps to reinforce the correct facial expression. The first sign we ever taught her was the 'OK' gesture (Thumb and index finger tips touching and forming an O shape with the other fingers extended) - indicating that she had done something well or had been a good girl, and we always accompanied this with a big smile, a nodding head and usually a food treat. If your Deaf dog comes to you as a puppy this is very useful for toilet training.
The number of signs you are able to use will depend on you and your dog, we only use about a dozen or so but some owners claim to have taught their dogs a lot more than this!
Be prepared from some strange looks from passers
by when you communicate using signs - some people find the concept
of a dog understanding sign language difficult to grasp!
When asked how we trained our deaf dog we replied to one enquirer
that we used sign language; he looked at us puzzled for a few
seconds and then asked "How do you get her to do that then?"
thinking that Dizzy was doing the signing back to us !!!!!
For further information about using sign language try Susan Cope Becker's excellent book 'Living with a Deaf Dog' which contains lots of helpful illustrations.
See the following link for further information:

