For failed Perception checks, the level design as such can indeed just leave visible hints / clues, which is sometimes the case already.
Currently, when I visibly fail a Perception check, I sort of know there is a hidden mine/trap on the road :P
But see if my character is not smart/attentive enough to find the trap, then he assumes there is no trap. If I show that there is something hidden in the area then I as the player know more than my character.
You could solve this cleverly. For example by saying you need a skill check of 15 to spot the trap but only a skill check of 10 to show signs of the trap (some pattern on the floor or drops of blood etc). Combine this with an intelligence check and your character knows something is off but not where. It would be annoying in a pen and paper but in a game you can role as much as you want in the background.
I just generally don't like when the player knows more than the character. The whole style of playing changes because you always want to know what you just missed.
