There are some ways to tell what Cobb is doing - if he can smell, he will make a sniffing noise at intervals which gets faster the closer the scent is. Also, his eyes are always looking in the direction of what he finds interesting, and intense ambience only plays if he is aggressive. Icons in the top right help with knowing your visibility/noise, but it's up to intuition to know if he can pick up on it.
That being said, I do think more ways to communicate these behaviors could help players and make Cobb feel more alive :P
(Btw, you can always see the rules in the pause menu if you forget what they were.)