I agree having an icon appear when targeting an ememy would be better idea than how the aggro icon is currently displayed.

Also if the player is much higher level than the enemy for it to be aggressive towards the player then the aggro icon shouldn't show. Example: I was passing by some of those yarzon type mobs and they were blue to me but were displaying the aggro icon so I thought I was still in the level range to be attacked. I ended up walking past them without any problem.

So really we should have another colour level that indicates "Too Weak" (grey) and the aggro icon should not be shown since the enemy is too low level to attack the player.