Signature weapons can be unlocked by doing certain challenges in-game. These weapons are powerful and have set attachments, but cannot be customized. They must be purchased.
AMR (Sniper Rifle) - Find 20 Relics
Bull (Shotgun) - Find 10 Relics
Bushman (Assault Rifle) - Activate all Radio Towers
Japanese Tanto (Melee Weapon Replacer) - Find 6 Letters of the Lost
Ripper (Light Machine Gun) - Survive 6 Trials of the Rakyat
Shadow (Pistol) - Take over 17 Encampments
Shredder (Sub-Machine Gun) - Collect 10 Memory Cards
Free Fall 5 Freefall more than 100m and live (Single Player only).
Inked Up 5 Earn 5 skill tattoos.
Fully Inked 30 Earn every tattoo by learning all the skills.
Money to Burn 15 Spend $5000 at the shop.
Aftermarket Junkie 20 Buy all attachments and paint jobs for one weapon.
Rebel With a Cause 10 Liberate 3 outposts.
Island Liberator 40 Liberate all outposts.
Unheard 20 Liberate an outpost without triggering an alarm.
Full Bars 20 Activate 9 radio towers.
Archeology 101 20 Gather a total of 60 relics.
Dead Letters 20 Gather all "Letters of the Lost".
Memory to Spare 20 Gather all the memory cards.
Jungle Journal 20 Unlock 50 entries in the Survivor Guide.
Bagged and Tagged 10 Complete a Path of the Hunter quest.
Road Trip 10 Complete a Supply Drop quest.
In Cold Blood 10 Complete a WANTED Dead quest.
Let the Trials Begin 10 Beat any Trial of the Rakyat score.
Poker Bully 20 Win $1500 playing poker.
Hunter Hunted 10 Lure and kill a predator.
Poacher 20 Hunt and skin a rare animal.
Artsy Craftsy 10 Craft 5 upgrades for your equipment.
Needle Exchange 15 Craft 25 syringes.
The Good Stuff 15 Craft a special syringe.
Say Hi to the Internet 10 Find the lost Hollywood star.
Heartless Pyro 10 Kill 50 enemies with the flamethrower (Single Player only).
Love the Boom 10 Kill 4 enemies simultaneously with one explosion (Single Player only).
Rock Always Wins 10 Fully distract 25 enemies with rocks (Single Player only).
Island Paparazzi 15 Tag 25 enemies using the camera (Single Player only).
Fearless or Stupid 15 Dive more than 60m (Single Player only).
Never Saw it Coming 20 Kill an enemy with a takedown from above from a glider, zipline or parachute (Single Player only).
Improper Use 5 Kill an enemy with the Repair Tool (Single Player only).
Toxophilite 10 Kill a target from 70m or more with the bow (Single Player only).
Here We Come 20 Complete "Ready or Not" Co-op map (Online/Offline).
Return to Sender 20 Complete "Sidetracked" Co-op map (Online/Offline).
Rocking the Boat 20 Complete "Overboard" Co-op map (Online/Offline).
Hide and Seek 20 Complete "Lights Out" Co-op map (Online/Offline).
Late Night Pick-up 20 Complete "Rush Hour" Co-op map (Online/Offline).
Getting Even 20 Complete "Payback" Co-op map (Online/Offline).