I think it's nice to have an agro icon, it may not be needed for veteran players but its nice for new players, and for future reference we know what will agro straight away rather than running up to a monster and finding out the hard way. It does look a bit much though, maybe adjust the size of the icon, or add it in to the '/check' window next to monster difficulty, and have it only display the agro icon if the monster is high enough to agro your current level.