I've just discovered a new tip today. Basically, when you're behind a box (the wood crate ones) and aim at an enemy through the box, the enemy's tag will display. Same applies to when an enemy is behind a box! The former method is useful against snipers who are aiming in sight. They cannot see you because you're behind a box! Just shoot away through the wood crate!
The latter method is useful against people who are hiding behind boxes.

I'm not sure if it's considered as an exploit, because your bullets can penetrate enemies through a box, even though the enemy tag will display when in fact that you cannot see the enemy (directly).