The Green Hornet and Kato are a pair of masked vigilantes, similar to Batman and Robin although generally less well-known. To more easily penetrate criminal organizations they masqueraded a criminal mastermind and his chief side-kick. The Hornet was a creation of George Trendle, and distantly related to another Trendle creation, the more famous Lone Ranger. This cross-over appearance was early viral marketing for the 1966-1967 television series about the character.
Colonel Gumm's henchmen all have names drawn from stamp terminology. A "block" is a group of stamps, often thematically related, issued at the same time and from the same pressing. "Canceled" takes his name from what the post office does to prevent the reuse of a stamp: a cancellation mark invalidates the document. Finally, "Reprint" (Gumm's chief forger) takes his name from the process of creating additional stamps when needed - something he's kind of doing, in a criminal way...
Roger C. Carmel is the only actor who played a major villain who did not receive front billing as a "Special Guest Villain." Instead, The Green Hornet and Kato received this billing, as "Special Guest Hero" and "Special Guest Assistant Hero" respectively. For much of the story the question was what side of the law they were on, but viewers knew from the credits. A few lines at the end of the second part suggest Batman had pierced their deception - or perhaps he was only speculating.
Britt Reid: The Green Hornet? In Gotham City? Well, that shouldn't disturb you, Batman. Your name is legend among crime-fighters.
Batman: Legends are sometimes overrated, Mr. Reid.
Robin: Fine time for the Batcomputer to let us down!
Batman: It's not the machine's fault, old chum. We overlooked one thing when we constructed it--a duel-identity Batsensor.
Robin: Holy oversight!
Britt Reid: Oh, that is beautiful--beautiful. What's it called?
1st Model: Shirley.
Britt Reid: A peignoir named Shirley?
1st Model: No--I'm Shirley. Lingerie bazaar--off at six.
Bruce: Yes, very lovely. What size is it?
2nd Model: Five five five, dash, five five five five.
Bruce: Size five million, five hundred fifty-five thousand, five hundred fifty-five?
2nd Model: No. That's my telephone number. Ask for June.
Batman: You satanic, mad stamp man!
Colonel Gumm: Satanic, Batman? Who knows? But mad stamp man? Perhaps!
Narrator: The Green Hornet and Kato?? Blocked, gummed, and perforated?? And then thumbtacked to a wall as collectors' items!! With Batman and Robin to follow?? When they're unglued from the undetachable glue pad!! Don't stampede!! Stay close to your stamping grounds!! Tomorrow! Same Bat-Time, Same Bat-Channel!