Let me start by saying when it comes to people with autism, there is not one-fit-all answer. Using sign language as the main method of communication is no exception; every child is different and the decision should be accordingly. However, for those who are non-verbal and who usually tend to be on the severe end of the spectrum, I don't believe that sign language is the way to go.
Using sign language requires certain skills which are often lacking in children with autism and need to be taught in isolation at first such as imitation, eye-hand coordination, and fine motor skills.
Often times, we see some basic signs taught to the child such as stop, wait, more, eat, cookie, etc. These can be extremely beneficial and helpful to the child but are limited and most of times are not expanded to a full language.
Other issues with choosing sign language as the main communication method for non-verbal autism has to do with the characteristics of autism itself as sign language is a sophisticated method and does require a certain level of executive functioning. The child has to know that signing is not visible in the dark and it does require an audience. I have often find my child pointing or signing while he is in his room and I am somewhere else in the house. Perspective taking and theory of mind play a role of how sign language can be effective.
Finally, the general population does not know sign language and is better to consider a more universal method of communication such as speech devices and typing which have their own limitations as well but are more promising and have unlimited potential.
M.Ed. Special Education/ Autism Intervention
As a mother of a non-verbal son with autism , I often hear people telling me: " You are an angel " or " I don't know how you do it " or "I don't know what would I do if I were you??!", etc. I have to admit that I feel very uncomfortable hearing that because caring for my son is the most natural thing that comes to mind and yes it is very challenging and difficult at times, but my answer to all...and to the question of "how I do it?" is I get up every morning and DECIDE that I have to do it. I put one foot in front of the other and go, and I would assume that every one can do that if they DECIDE to do it as well regardless of the circumstances because to me it is not just an obligation but it is an honor and a privilege that I am entrusted to care for someone so vulnerable like my son, and as someone once said "the measure of a civilization is how it treats its weakest members.".
When my son was insisting on closing every door we open, I used that to teach him "open" and "close". I also would sabotage the environment where I would open doors on purpose so he would ask me to close it using his Dynavox (speech device).. That worked specially well on the kitchen cabinets where he could not reach them to close them himself. In essence , instead of looking at his obsession with closing doors as a negative, you could turn it into a positive and a teaching opportunity.
The same goes for those on the spectrum with special interest. Try to incorporate their interest in the teaching materials. When I was teaching my son how to do 'word search', I took advantage of his interest in Disney characters and used them as words to search for in the puzzle. I did the same when teaching him spelling, reading, and typing.
Another application of turning a lemon into lemonade or a disability into an ability ....