About Thresh's souls

Why is it that enemies can see the souls of a Thresh? This is a huge giveaway if he's waiting in the wings to land a hook from the brush - and is given away by a soul spawning from a minion kill.

I know that it's a goal of League of Legends to have clarity, and being able to see why your enemy is getting stronger is important. So why not have enemies only be able to see the souls of your team's Thresh if they see him when the soul is released? Or something similar?