This page lists the Easter eggs that can be found in Hitman: Contracts.
Once the player obtains Orthmeyer's Keycard from Lee Hong's office in The Wang Fou Incident, return to the asylum (by playing Asylum Aftermath). When you find the Dual Golden Desert Eagles and a minigun, continue down the room until the end. The player will be greeted by multiple tanks, which contain clones of Agent 47.
It is assumed that these are the original clones that The Five Fathers were originally going to get, before Dr. Ort-Meyer sent Agent 47 to kill them. It can also be inferred that these clones are fully grown holders of the Father's DNA, which Ort-Meyer would use to create future clones.
If you stand close enough to The Girl's corpse on the second floor, you can hear laughter. You can hear the same laughter if you stand near the building across the street from the hotel in "Hunter and Hunted".
Licensed Song (#1)
Also in the room with The Girl's corpse, a picture of Jesper Kyd can be seen on the shrine. Kyd composed the music for Hitman: Contracts.
Licensed Song (#2)
In the room where Alistair Beldingford and his friend are, the song playing on the gramophone is "A Different Kind of Love" by Dick Walter.
The Jungle God
On a wall in the manor, you can find three heads of a jaguar, a reference to the Codename 47 mission The Jungle God.
Jesper Kyd #2
Giles Northcott's model has a strong resemblance to Jesper Kyd.
You can find the Ghost of a dead resident in six different locations in the mission Traditions of the Trade. To find the hallway where the ghost is located, go to the hallway on the right of the ground level and keep on walking until you see a door with a sign on it saying "Wing Closed", either pick the lock of this door or open it with the Master Key. After you have opened the door then go left and open the double doors. Once you walk through the doorway you will be in a gray hallway. Each room in this hallway contains a mirror, and the ghost will appear in all of them. Aside from being able to take out the ghost with the Fiber Wire, if you drag it to the body in the "murder room", it will eventually disappear and never reappear anywhere else. Additionally, if you shoot the area above the bath or shower where he appears, blood will appear as if shooting a live enemy.
Terminator's Box of Roses (#2)
There is a box of roses in the florists shop, on the desk. Picking it up and selecting it from the inventory will show Agent 47 flipping the box, and pulling out a SPAS-12 in a shade of roses. This is a reference to "Terminator 2", where the Terminator retrieves a lever-action shotgun from a box of roses.
In Slaying a Dragon, in the streets, there is a building with a Yin-Yang sign. If you shoot the white circle of the black side of the Yin-Yang symbol, the information box will read "HELLO? OBSERVE THE CONTENTS OF MY EASTER EGG, SMALL CHILD!".
After that, go to the negotiators of the Blue Lotus Triad and the Red Dragon Triad at the park. Above their heads there will be poorly cut out dialogue balloons with "HELLO POKEY" over the Blue Lotus' and "YES" written on the Red Dragon's. If you kill the Red Dragon negotiator and the Blue Lotus negotiator notices you, he will flee to his limo, and the balloon written "HELLO POKEY" will appear when he reaches the limo. It is in reference to this comic strip.
"I'd like to use the washroom."
In the Hong Kong mission The Seafood Massacre, there is a reference to the rather awkward line "I need to use the bathroom" when 47 talks to a bartender.
The bartender with the red shades in "Rendezvous in Rotterdam" has an obtainable disguise, unlike the same looking one in "Deadly Cargo". Switching into first person in this disguise will have an interesting effect, different indoors and outdoors. Unfortunately, this effect was removed from the re-releases and the Steam version.
This may be another "Terminator" reference, as all Terminators see everything in red, and Arnold Schwarzenegger's Terminator is known for wearing sunglasses.
In the mission "Rendezvous in Rotterdam", when you go to the room where the Biker gang's President's office is located; just opposite to the office there is a room where a bald man is standing. Go to the last room in the corridor and you will see a chair and a table in placed and the room is full of tattoo drawings. Enter the room and look in one of the tattoo boards hung up in the wall.
The player will see the Hitman Insignia. Beside the insignia you will see the logo of Io-Interactive's Freedom Fighters a hand holding a Molotov cocktail and finally you will see the Io-Interactive logo beside the Freedom Fighters logo along with drawings of other tattoos.
Licensed Track (#3)
The song that can be heard on the entire first floor of the HQ is "Immortal" by Clutch.
Licensed Track #4
The song playing in the Dirty Rabbit strip club is "Walking Dead" by Puressence.
Licensed Song (#5)
In the room with the dead drug addict and a cop outside, the song playing on the radio is "Le Souteneur (Pimp)" by Faf LaRage.
Other easter eggs
Ort-Meyer's dead body
In the main menu of Contracts, if you look very closely to the left, you can see a dead body. That body is the one of the late Dr. Ort-Meyer, which 47 killed at the end of Codename 47.