How to Unlock the Hammer and Sickle in Warzone

They leaked the challenges to unlock the Sickle and Hammer:

• Multiplayer / Warzone: Get a melee kill and a Tomahawk or Throwing Knife kill in a single life in XX different completed matches.
• Zombies: Using melee weapons, kill XX special or elite enemies that your Frenzied Guard mocks.
• Buy a bundle where melee weapons are already unlocked.

Sickle and Hammer Added to the Game

At this stage, it is only available in Cold War, it will be available in Warzone later.

• Unlock through a challenge (get melee and Tomahawk kills in 15 matches in one life) or buy it in the store.

I wouldn’t recommend doing either. Vanguard launches in 2 days.