At the end of the game, depending on how many people you kill, the type of people/animals killed, the type of weapon used, the speed you played through the game, or the difficulty you play the game on, the final score sheet will generate a summary based on how your playthrough meets one of those conditions.

In particular, in regards to how many people you kill, beating the game without killing anybody will give you the summary "Thank you for playing, JESUS.", while beating the game presumably killing everything you can will give you the summary "Congratulations, SATAN.".
Contributed by MehDeletingLater
In June 2016, an update was added to Postal 2, 13 years after release, this update added a way to enter the closed video game store which stated it would reopen in June of 2016, inside the player can find a VR headset similar to the HTC Vive. Putting the headset on will bring the player to a virtual reality store named "Steme", which sells copies of Postal Redux, and parody versions of popular steam games. (including Counter Strike: Global Offensive and Doom) The cashier will also give the player tips from the future, like betting on the Red Sox and not buying Postal 3. A Sports Almanac can also be seen outside the store, as a reference to Back To The Future.
Contributed by Liraxus
Owning or distributing Postal 2 in New Zealand is punishable by imprisonment.
Contributed by Mass Distraction
Children can be seen watching footage of this game in the music video for The Black Eyed Peas song "Where Is The Love".
Contributed by IkiFoo