I think it should be like when you hit an enemy it does -10% damage but you can track them through there outline. It would be like if someone on your team had the enemy intelligence, they would have an outline which you can see through walls. This effect would stay on them until they picked up a health kit or say 10, or 20 seconds had past. Everyone on your team would be able to see the outline so it would be good for competitive.
Also if you headshot an enemy the effect would last longer and only wear off if you use a full health kit and not one of the bottles and there would be no time limit. Also on headshot the enemy would have a bleed effect for a bit.
The cons of this weapon would be that enemy snipers do 25% more damage to you on body shots and insta-kill you with a headshot/neckshot 100% of the time.