To begin the new season, when the opening credits show the arrow we hear the sound of a jail cell door closing.
At approximately 39 mins, next to Oliver's photo of William and Felicity, there is a copy of The Count of Monte Cristo. Alexandre Dumas' classic tale of wrongful imprisonment, and eventual exacted revenge.
Felicity is seen working at Radu's Coffee Shop. Radu's Coffeeshop is frequented by Green Lantern Kyle Rayner in Greenwich Village in DC Comics.
Inmate 4587 is in reference to Oliver Queens prison number. As in prison you are never called by your real name as that would be compassionate, instead they are only called by your prison number by all of the guards, staff and prison personnel.