Is stacking cans really a sign of Asperger's? Wikipedia says:


  
  
  People with Asperger syndrome often display restricted or specialized
  interests, such as this boy's interest in stacking cans.


How predictive is this of Asperger's: What percentage of normal boys and boys with Asperger's display this type of behavior, respectively?
Symptoms of Asperger’s Syndrome


difficulty recognizing social cues
awkward body language
social isolation
aloofness
fixation on certain objects


The picture (and idea) that “stacking cans” is in itself a sign of Asperger’s is misleading at best.
One could just as easily say this child is making “a tower”, a common activity amongst children.

Asperger at Psychotherapy Collective

Stacking objects can be a child development tool.

Childhood development tools