I wouldn't say Herobrine is an amazing legend or anything near it. Some guy edited an image and said "Wait what? There's a person there!" and then it was eventually proven to be a hoax. Of course there's stories on how he's some evil or good being that watches you, but that's about the extent of it.
I mean yeah sometimes people claim Herobrine to do things like break parts of trees or leave a house or whatever, but that's not exactly interesting.
As for cryptic messages for Herobrine, it'd kind of break the game's lore-free area. Pretty much everything is shrouded in mystery. Those temples, the ocean monuments, the mineshafts... Who built them, why? What happened to them? What purpose did they serve? We have literally nothing to go on and that's what gives Minecraft its freedom. There are no rules and there are no specifics.
If we added cryptic messages specifically towards Herobrine, well whats the point if we all know who it's about? And if we didn't, well it'd eventually be figured out "Oh wait I think that's herobrine!". That's the great part about the mysteries in Minecraft. No one is able to come with a clear resolution and it will forever be a mystery. Herobrine is already clear on what he is and what he does, so there's nothing really to hide about him.