At what point do you start looking into evaluation?
My 26 month old son has always been somewhat slow about speaking. He's otherwise on track developmentally, isn't autistic, can follow complex directions (and has been able to since at least 14 months), and identifies objects (pointing to the correct picture when I ask if he can find something) I had no idea he knew about. I haven't seen any reason to believe he has hearing problems. He doesn't regularly hear any language other than English.
He is continually saying new words, but will often say something once and then not again. For the most part, his words are unclear, and often only recognizable in context. He has maybe 10-20 words that he says on a regular basis. Very rarely (like maybe once every few weeks) he'll pop out with two or three words together. He babbles incomprehensibly all the time.
We tried doing baby signs with similar results - except for a few words he found useful (like "more", which he still uses, especially when prompted), he'd occasionally make a sign for a brief time and then stop doing it.
I'm not particularly worried - I expect he's just a late talker and he'll catch up fine on his own if we wait. But I also don't want to take the wait and see approach if there is a problem that could be helped, especially as I've heard that the waiting list for evaluation is long. His doctor doesn't seem to think there is a problem, but this doctor tends to be very rushed (didn't even have him get undressed at his recent appointment, which was the first with this particular doctor!), but a friend who is a pediatric neurologist did suggest getting him evaluated.