When Ann brings her laptop to the hearing (to play Leslie's video of her and Ben), the laptop case she is using is the one Mark gave her years ago. This is one of only a very few references to Mark after he left the government.
The portrait on the wall of the Pawnee hearing room of the man whose face was scarred by an explosion is actually a retouched 1859 self-portrait of Jean-Auguste-Dominique Ingres, a French painter (1780 - 1867).
The trivia item below may give away important plot points.
Viewers learn when "Jerry" is on the stand during Leslie's trial that his real name is Gary. In fact, during the previous episode Jerry showed his Parks and Rec ID card to Tom, and his first name is given as "Garry."