Heck I used to know their lingo well 12 years ago, but haven't used it since!
3 caw's (not too long or drawn out) seems to be a locator call and might get another crow to answer and maybe head your way. I had good luck with a 'question and answer' type of calling starting with one normal caw immediately followed by two short quick high-pitched 'yips' (caawww yip-yip - only way I can describe it) that sounds like a 'where are you?' question, followed by the 3 slow caw's. It usually got a curious crow or two headed my way. The fast caws I think mean slightly different things depending on the rate and tone. Best thing to do is go out in full camo and sit quietly and listen to the flocks in their normal behavior (without you spooking them). If they find a hawk or owl they will go nuts, those are good sounds to learn, since when crows get their dander up they lose all sense of being careful.
