Okay, here's my rule of thumb on both ameraucanas and EEs (and keep in mind that EEs can be weird and sometimes don't follow the rules)-
Male combs have three ridges side by side. On the little ones the initial comb is wider than on the girls and as they grow you can see three rows pop up. Their combs turn red sooner than the females. For some reason all my EE boys have turned red pretty early on. With the Ameraucanas they can sometimes be slow to redden up.
Female combs have a single ridge. When they are little you don't really see a comb at all and as they grow it comes up later and is narrower than on the boys.
I have gotten to the point that I can guess pretty accurately at about two weeks. I'm not always right with the EEs especially as you sometimes get sneaky ones, but overall the comb ridge trick is fairly accurate.