Among much research and many hours of play I did find some easter eggs in GTA IV
among them some pictures:
Manhunt for a pair of one character
Carcer City Manhunt on a shirt
reference to the film Full Metal Jacket
San Andreas in Shirt GTA IV
Brazilian store in GTA IV and Garfield:
the total found 113 easter eggs so far and there is still much more to discover in Liberty City
other easter eggs on the Blog:
http://gtabrteam.blogspot.com/search/label/IV%20-%20Easter%20Eggs