Simple example - there is a rogue in the party with high Perception and the DC for a trap in the room is high enough that only he can see it.

Or, more confusing still, the rogue also has high Sleight of Hand and lifts a guard's keys. Neither the guard not the players have a high enough Perception to detect the act.

Since the skills are supposed to represent individual knowledge, what's the best way to handle these scenarios? In the first, since only the rogue knows of the trap it should be left to that player whether they want to tell the party (IMO). And in the second, again the rogue should get to decide who knows about the theft (the DM should know).

Post-it notes? Texting? Just say it aloud but don't let players act on information they're not supposed to have? I want my players to have agency and take advantage of their skills, but situations like this are tricky for me.