Some signs are said to be apparent during infancy, but they usually become more apparent (and more reliable as a diagnostic indicator) in early childhood. Most pediatricians perform some type of developmental screening during the Well Baby Checkups, to ensure they are meeting developmental milestones at age-appropriate times. If you have concerns about your child's development, please share those concerns with your child's doctor.
Autism Spectrum Disorder, as it's title indicates, occurs on a spectrum; meaning that characteristics and severity can vary widely. The signs of Autism typically fall under 4 broad categories: Communication, Social Behavior, Stereotypical Behavior and Other Behaviors. Please check out the links below for more specific information from the National Institutes of Health and the Centers for Disease Control and Prevention (CDC) regarding signs and characteristics of Autism.
Since characteristics can vary so widely, your child showing some of these characteristics does not necessarily mean your child has Autism. However, if your child is showing some of these characteristics, please discuss this with your child's Pediatrician to determine the need for an evaluation.