These weapons are kind of hidden in the Create-a-Class menu.
Call of Duty Black Ops 4 has traded in Weapon Variants for Signature Weapons this time around. Equipping them isn’t as straight forward as you might think as the only way to select them is in the create a class menu and the only indicator that you have them is a small arrow above the default weapons.
When you unlock a Signature Weapon in Black Ops 4, whether that be through purchasing a special edition of the game or unlocking it through the Contraband Tier System, the weapon will be available in the create-a-class screen under your Primary Weapons tab.
Whichever Signature Weapon that you have will basically be a cosmetic variant of the base weapon. The Damascus, for example, is unlocked by reaching Tier 105. To select the Damascus you would go to the SMG tab and then press up on the d-pad or left analog stick to access a hidden menu above the gun that gives you access to your Signature Weapons.
Once you’ve got a Signature Weapon selected you’ll have access to Reactive and Mastercraft skin challenges for that weapon. Not all weapons currently have Signature alternatives at the moment. Treyarch appears to be rolling these out exclusively as rewards for completing Tiers of the Contraband system, with players needing to do some heavy grinding to get them during Operation First Strike.
It’s expected that more weapons are released in future Black Ops 4 Seasons. When they are, just make sure to press up on the d-pad or left analog stick when trying to equip your Signature Weapons that you’ve unlocked.
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Attack of the Fanboy / GAME GUIDES / Black Ops 4 How to Equip Signature Weapons