Source: Waterdeep - Dragon Heist

Wondrous item, rare (requires attunement by someone designated by the Open Lord of Waterdeep)

A Badge of the Watch is given only to those who have earned the trust of the Open Lord of Waterdeep. The badge, signifying the rank of captain in Waterdeep's City Watch, bears the emblem of Waterdeep and is meant to be worn or carried.

While wearing the badge, you gain a +2 bonus to AC if you aren't using a shield.

If the badge is more than 5 feet away from you for more than 1 minute, it vanishes and harmlessly reappears on a surface within 5 feet of the Open Lord. While holding the badge, the Open Lord knows your location, provided the two of you are on the same plane of existence and your attunement to the badge hasn't ended.

As an action, the Open Lord can touch the badge and end your attunement to it.