go to www.autismspeaks.org and check it out
Since autism is a spectrum disorder, and because so many symptoms individually can be attributed to other syndroms and even normal behavior, it is difficult to say. any search on the internet of symptoms of autism will tell you that it's different for all cases. there are however some warning signs. For example, repetitive behaviors, delayed social and communication skills, hyper or hypo sensitivties, etc... If you have any concerns, i suggest you speak to your pediatrician.