Complete the following tasks to get the corresponding Emblems. There are 40 in total and each ones brings a different reward, that might be a special item or weapon.

Ant Emblem
Shake down 50 enemies for items

Assassin's Emblem
Complete the game with less than 25 alerts and more than 50 of both knife kills and CQC holds. This will give you the ALtair Costume from Assassin's Creed.

Bear Emblem
Choke 100 enemies to death

Bee Emblem
Utilise the Scanning Plug S or Syringe on 50 enemies

Big Boss Emblem
Complete the game in less than 5 hours on the highest difficulty with no deaths, no alerts, no kills, no recovery items (rations, regains or noodles) , no stealth suit and no bandanna items. This will give you the Big Boss face camo.

Blue Bird Emblem
Give away 50 items to friendly soldiers

Centipede Emblem
Get less than 75 alert phases, less than 250 kills, and over 25 continues.

Chicken Emblem
Get over 150 alert phases, more than 500 kills, more than 50 continues, use more than 50 recovery items (rations, regains or noodles) and complete the game in over 35 hours.

Cow Emblem
Activate over 100 alerts

Crocodile Emblem
Do more than 400 kills

Eagle Emblem
Make 150 headshots

Fox Emblem
Complete the game in less than 6 hours on at least normal mode with no deaths, kills, recovery items (rations, regains or noodles) , stealth suit or bandana items and with less than 5 alerts

Fox Hound Emblem
Complete the game in less than 5.5 hours on at least normal mode with no deaths, kills, recovery items (rations, regains or noodles) , stealth suit or bandana items and with less than 4 alerts

Frog Emblem
Make over 200 dives or rolls

Gecko Emblem
Be pressed against walls for a total of at least 1 hour

Giant Panda Emblem
Complete the game in more than 30 hours

Gibbon Emblem
Hold up 50 enemies

Hawk Emblem
Be admired by 25 friendly soldiers

Hog Emblem
Make 10 combat highs

Hound Emblem
Complete the game in less than 6.5 hours on at least normal mode with no deaths, kills, recovery items (rations, regains or noodles) , stealth suit or bandana items and with less than 4 alerts

Hyena Emblem
Pick up 400 dropped weapons

Inch Worm Emblem
Have a total crawl time of more than one hour

Jaguar Emblem
Get more than 75 alert phases, less than 250 kills, and less than 25 continues

Leopard Emblem
Get more than 75 alert phases, less than 250 kills, and over 25 continues

Little Gray Emblem
Collect all 69 weapons

Lobster Emblem
Crouch for at least 2.5 hours in total

Mantis Emblem
Complete the game in less than 5 hours on at least normal mode with no alerts activated, continues, or recovery items (rations, regains or noodles)

Octopus Emblem
Complete the game without activating any alert phases

Panther Emblem
Get over 75 alert phases, more than 250 kills, and less than 25 continues.

Pig Emblem
Use at least 50 recovery items

Pigeon Emblem
Complete the game with no kills. This will give you the bandana. Alternatively you can also receive the bandanna from Drebin for 5,000,000 DP after you complete a new game + (that would be a new game after you have completed the game at least once)

Puma Emblem
Have less than 75 alert phases, make less than 250 kills, and less than 25 continues

Rabbit Emblem
Look at 100 Playboy pages

Raven Emblem
Complete the game in under 5 hours

Scarab Emblem
Roll forward over 100 times

Scorpion Emblem
Have less than 75 alert Phases, less than 250 kills, and have less than 25 continues in total.

Spider Emblem
Have less than 75 alert phases, over 250 kills, and over 25 continues.

Tarantula Emblem
Get less than 75 alert phases, make over 250 kills, continue more than 25 times.

Tortoise Emblem
Hide in either an oil drum or card board box for at least 60 minutes in total.

Wolf Emblem
Complete the game with no continues, or recovery items (rations, regains or noodles)

When you have beaten the game once on any difficulty setting go to the 'Extras' screen and then 'Password' and enter the following passwords to unlock the corresponding iPod song.

Unlock 'Gekko' iPod Song:
Enter the password george

Unlocks 'Midnight Shadow' iPod Song:
Enter the password theodore

Unlock 'Desperate Chase' iPod Song:
Enter the password thomas

Unlocks 'Mobs Alive' iPod Song:
Enter the password abraham

If you enter the following codes instead of the code Otacon tells you to at Shadow Moses you'll receive the indicated bonus after the 'Access Denied' scene.

Unlock 100,000 DP:
Enter the code 14893

Unlock iPod song:
Enter the code 13462

Unlock iPod song:
Enter the code 78925