This page lists the Easter eggs in Hitman 2: Silent Assassin.
FCK Danish Champions
During this mission the newspaper which is located in the offices say "FCK Danish Champions 2001".
On the 3rd floor, near the exclamation point, there is a book with the sentence "Vamos Arregaçar". It's in Portuguese, and means "Let's put all down" or "Let's kill everybody".
"The Jungle God"
There are two Jaguar Hunting trophies and a Jaguar skin hung over the walls of the main hall. This is in reference to Tezcatlipoca, "The Jungle God", from Hitman: Codename 47 suggesting that it was killed.
Commander Keen Eye
At the top of the table in Charlie's room is a Dopefish, that is a reference to the Commander Keen video game series developed by id Software in the early 1990s.