In InFamous, near the Centerplex Movie Theater, there will be a listing of movies that are showing at the theater. One of the movie Titles is "Sly Cooper 4", you can also find "Honor Among Thieves" under it, which is a reference to Sly 3. If you can find a way to zoom up on Cole's backpack, you can see the Sly logo from the original game on the bottom left corner of his backpack.