witcher

Warrant is a quest item in The Witcher 3: Wild Hunt, dropped by three of the witch hunters encountered during the Novigrad, Closed City - the two ambushing Geralt in the house Lussi leads him to, and one of the two attacking Wallter behind Crippled Kate's.

Reading it provides the clues necessary for Geralt to know what to do with the keys, and is one way to start or resume the quest as:

Even if you somehow missed getting the warrant though, don't worry - the letter about treasure serves the same purpose and isn't missable.

Journal entry

WANTED: Three bandits in possession of magic contraband. Objects are dangerous, banned, to be destroyed immediately.
Lussi, known as the Fox. Hiding on Temple Isle, near the bridge.
Fritz, hiding near the Crooked House.
Wallter, last seen in the Lacehalls, near the Putrid Grove.
Bandits are to be apprehended or, if they resist, killed where they stand.

Associated quest