Autism and Asperger's are specifically neurological conditions, and they manifest in a very wide spectrum. I have Asperger's, which is commonly considered a form of autism, although I do not (as too the man the condition is named for). Asperger's is often seen as a social developmental disorder, but in truth it's far more complex (and interesting) than that (and it's not necessarily a "disorder" either). Social difficulties arise due to fundamental differences in how the individual thinks, percieves, understands, deduces and recalls. People with Asperger's have a "high systematizing" brain incline to learning and retaining vast amounts of information, and tend ot develop a subconcious mental preference for object over people at a very early age. Normally Asperger's begins to show around 3 or 4. Hence why we often don't develop socially in the conventional way. In addition, people with Asperger's often have above avergae to genius IQ scores, superior verbal skills (despite their lack of social interest or activity) and problem solving skills, and may have savant-like talents or have a overriding obsession-like interest in very narrow or very unusual things. There is often an overemphasis on logic, rules and order, as teh indivudal often has difficulties coping with change and less orderly or consistant things like the "unwritten" laws of social interaction. Asperger's often is comorbid with other conditions such as Exective Function Disorder, OCD, depression, anemia, allergies, anxiety disorders, GI disorders and sensory hypersensitivities. Physical traits common (butnot universal) are an strangely shaped head (larger or wider than normal), strange or very intense looking eyes, weight extremes, and ambiguity due to underdevelopment of secondary sex traits or the person appears androgynous. People with Asperger's often feel like they are not of the same species as "neurotypical" people, and often feel very alienated by society. In many cases, we are bullied, abused (girls with Asperger's have a higher rate of molestation, for example), taken advantage of or harshly treated by others, who intutively sense we are "odd" or not as socially aware/adept as others. All of this of course only compounds our social difficulties.
While my chart doesn't seem extraordinary at first, there is a preponderence of both air and mutable, with a lot of bodies in Gemini, which falls on my MC. In addition to having Sun conjunct Mercury in gem in the 10th, I have Venus and several asteroids in Gemini. Furthermore, all my planets are part of one or more aspect configurations, and all those configs involve one or more of my planets in Gemini. Furthermore, Mercury is but my chart ruler (Virgo ASC) and prime dispositor, as well as being the only essentially dignitified planet and the most accidentally dignified as well.
There's an overwhelming emphasis on Gemini, Mercury and my MC area in my chart, but this is counterweighed by two singletons - Uranus and Neptune - and the fact that that these singeltons rule two of my personal planets - Auqa Mars and Pisces moon. So there's a strong Gemini theme (neurological), that's interwoven with a heavy-duty Uranian theme (cerebral, nonconformity, detachment) and a Neptunian undercurrent (extremism, hypersensitivity, alienation). Both Singletons aspect that gemini region so this all comes back to my MC (life path, social intergration, social enterprise). Granted this is not a blueprint for all Asperger's, but it does sum up very nicely how my Apsperger's manifests.
SInce both autism and Asperger's are neurological conditions that affect the most primal and fundamental functions of the brain, and because the brain is an individual as anything else about us, I am very sceptical that there's one broadsweeping indicator, or even a simple complexus of indicators for these conditions. I think it needs to be on a chart by chart basis, and certianly considering Mercury as a focal point would be a sensible strating point.