Listed below are all the unlockables in the game along with what you have you 
to do to get them and in what level.

Result                     Code
-------------------------------
25 To Life Decal         - Level 1: Take Two Human Shields
ATF Decals               - Level 5: Arrest 4 dealers
Bank Robbing Outfit      - Level 3: Escape to your Getaway car
Barbed Wire Hat          - Level 2: Defeat 25 enemies
Big "Dawg" Tattoo        - Level 6: Achieve 30 percent accuracy
Big Mustache             - Level 5: Achieve 25 percent accuracy
Black Bandanna           - Level 2: Cover up 4 tags
Black Gloves             - Level 11: Get into 5 ATM's
Bulldog Chain            - Level 12: Find all 5 secret stashes
Camo Pants               - Level 9: Defeat 32 enemies
Chest Flame Tattoo       - Level 9: Get 16 headshots
Chest Tattoo             - Level 8: Defeat 45 enemies
Chinese Pain Tattoo      - Level 10: Protect Lazarus
Clock Cap Decal          - Level 7: Defeat 60 enemies
Daz and Tech Tattoo      - Level 12: Kill Shaun
DJ Envy Outfit           - Level 5: Get to the subway
Federates Outfit         - Level 8: Escape with loot
Flaming Beanie           - Level 1: Defeat 20 enemies
Freeze's Mall Outfit     - Level 11: Finish level
Freeze's Prison Outfit   - Level 10: Finish level
Freeze's Starting Outfit - Level 1: Get to your car
Full Tactical Harness    - Level 6: Free a police officer
G Cap Decal              - Level 12: Defeat 30 enemies
Gold Earrings            - Level 3: Shoot all ATMs
Holster                  - Level 4: Achieve 20 percent accuracy
Kneepads                 - Level 4: Arrest 5 felon criminals
Mexican Flag Bandanna    - Level 7: Paint over 4 Gang tags
No Parole Decal          - Level 10: Defeat 30 enemies
Officers Williams        - Level 4: Take the evidence to Mendoza's car
Red Hightops             - Level 11: Complete this level without dying
Rick Ta Life outfit      - Level 2: Return to your car
Riot Helmet              - Level 5: Get 8 head shots
Scorpion Black Tattoo    - Level 8: Get 12 headshots
Shaun's Getaway Outfit   - Level 6: Trap Shaun in a subway traincar.
Shaun's TJ outfit        - Level 7: Find Riggs at the club
Sideburns                - Level 6: Defeat 24 enemies
Tactical Vest            - Level 4: Keep partner alive
Triple Bracelets         - Level 8: Rob five cash carts
Westside Knife Tat       - Level 3: Defeat 25 enemies