The card Jimmy Dix signs for Joe's daughter is a Pro Set Superbowl Super Heroes card. That set, which was produced by the only card company ever fully endorsed by the NFL, was made only in 1991 and featured stars of the NFL's biggest game. On that note, Damon Wayans has been asked for "Jimmy Dix's" autograph in real life...and given it.
In a "New Yorker" profile, producer Joel Silver said that the making of this film was "one of the three worst experiences of (his) life." Tony Scott also spoke about how miserable production was, largely because Silver and Bruce Willis took over the production, altered parts of Shane Black's script, and made him shoot scenes he hated under threat of being fired and having to forfeit his salary.
With this film, Shane Black became the first writer to sell a spec script for $1 million. According to Time Magazine, he was originally offered $2.25 million by Carolco Pictures, but decided to go with Warner Brothers. He went for the lower (but record-setting) bid of $1.75 million, so that he could work with Joel Silver, who had also produced his script for Lethal Weapon (1987). This record stood for 67 days until Carolco purchased a screenplay by Joe Eszterhas which became Basic Instinct (1992).
In the original script, the entire third act was set on water. Also, Hallenbeck's grudge with senator Baynard was completely different from the movie. In the script, Hallenbeck was working security for the Baynard family when Louis Baynard, President Baynard's son, kills a mother and her child in a drunken car accident. When Hallenbeck refuses to cover for the president's son, they plant half a kilo of crack cocaine in his house. Louis Baynard was also a villain in the script, and in the end both he and his father die.
The conversation between Joe and Jimmy about the $650 pants was taken from a deleted scene in Lethal Weapon (1987). Murtaugh's daughter is wearing an expensive dress for a New Year's Eve party and he asks, "It doesn't have a little TV in it?" She says, "no" and Murtaugh mutters, "I am very old."
The card that Darian gives Jimmie to autograph was produced by Pro Set, a trading card company based in Dallas,TX. The card is a fictitious one, but appears to be of similar design to a real set of cards made by Pro Set. In 1990, the company produced a Super Bowl commemorative set. Superbowl Supermen, the headline of the card, was a legit part of the set.