In exactly one case, several hours into the game, with not even the tiniest hint before that. But once it happens, the right thought should be "oh, I must watch for puzzles now, there will surely be some (if I'm not doing it already, because I always do that, even when there isn't any indication that there will be any)". Then I see where I failed, mine thought was "hmm, what's the point, why should I suddenly write something down? but if it says so...".
Seriously? Sensei's slightly amusing password, which suggests that he's really hopeless pervert (and that he doesn't know how to make secure passwords) sticks as something you should write down? Some random usernames in weird "radio noise" somehow seeping to the world from who knows where (or whatever is really happening) too? So out of curiosity what else does stick out? Did you write down how much Sensei paid for his hamburger? It could be important! Or it could be a trick question, because I have no idea if it was mentioned.
And what exactly should give player that idea? Remember, the event with address happens much later. So any time between the beginning and that moment? Or is it just default assumption, that in every game could be a puzzle? And when you finish it and there wasn't any, then oh well, just throw away the full notebook, take a new one, sharpen the pencil, and be ready for next one? Because one day it will be worth it!