I'm a big fan of the two prong approach: Early Intervention and medical evaluation by a developmental pediatrician. EI is great for identifying what delays a child has and providing needed services, but in many areas (such as mine) they cannot give a medical diagnosis. For us the process of getting the medical diagnosis took about six months, not counting the four month waiting list to see the DP. The DP ordered medical tests to rule out known chromosome disorders, metabolic disorders, seizure disorders, hearing problems, etc. DS also had a full eval by a child psychologist. The official diagnosis of autism was not given until everything else had been ruled out.
As for what behaviors we saw at age two, the most obvious was that DS was still non-verbal at that age. He also had hard time understanding what we said to him. He couldn't follow verbal directions unless it as something we said frequently.
Shortly after he turned two, DS started using his ABC blocks to spell four syllable words (helicopter, motorcycle, etc), but he still did not talk at all. At that point we had to face the fact that his development had taken an unusual turn. (DS has Hyperlexia as feature of his autism.)
Additionally, DS had fine gross motor delays, although we didn't realize it until EI pointed it out. I knew that he was behind in fine motor skills, as I remember telling the doctor that DS still couldn't take his socks off, I just didn't realize that he had real delays in that area. Also, DS did a lot of stimming: staring at ceiling fans, waving his fingers in front of his face, making odd noises, etc. He had sensory issues including fears of certain noises, dislike of getting his hands dirty, a need for certain types of movement.
This is a really hard stage that you are in, when you are trying to figure out what's typical for the age and what signifies a problem.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong