In the comics, Guardian's real name was Jim Harper and at one time worked for Cadmus.
When Mon-El is fighting the Parasite, he wears a red T-shirt and a blue jacket, the opposite of Clark Kent in Smallville (2001). In the DC Comics, Mon-El's costume is red with a blue cape, the opposite of Superman's.
The side of Winn's back-up van says "Star-Spangled Deliveries since 1942" this is in direct correlation with "Guardian"'s first appearance in Star-Spangled Comics #7 (the April 1942 issue)
The first live action appearance of the Guardian.
Jason Gray-Stanford's character in this episode is named Rand. His character's name on Monk was Randy, short for Randall.