My son has autism, and he talked quite early. It's a series of things they will look at. There are a few very simple things you can do to rule out autism in a child of three.
1. Call him by name. Does he immediately look up or in the direction of the person calling his name? If not, how many times must you call him before he responds
2. Does he play "pretend?" - If you give him a cell phone, will he pick it up and pretend to 'talk' like mommy? If you put him in a play kitchen, will he pretend to cook, or does he just bang things around?
3. lastly, does he have something called, joint attention? This is when he will look at something, and look to you, and then look back at the thing, to see if you are also paying attention to it. Does he point things out just to show you how "cool" something is? Not becuase he wants you to do something?
If he does each of those things, chances are pretty stinkin good you have a typical kiddo....