After unlocking the weapon, they may be purchased from the store or any self-service weapon locker.
Signature weapons are usually unlocked by completing certain objectives. How do you get signature weapons in Far Cry 3? Purchasing the maps for Items in each are will cause relic icons to appear on the map regardless of distance. Collecting 60 will complete the achievement or trophy (you do not need all 120). Collecting 30 will unlock two signature weapons and the Untouchable recipe. What happens when you collect all relics in Far Cry 3?