Continuity Nod/Comic Books

Examples of Continuity Nods in Comic Books include:

Too many to count in The Sandman, but the most memorable is the "Endless Nights" story, "The Heart of A Star"—Superman's ultimate origin is revealed to be a conversation between Krypton's sun and the first personification of Despair on the nature of beauty.
- Don't expect this to ever be considered official DC Universe continuity however, as it basically says that Superman only survived so he could feel the despair of being the last Kryptonian.
- This story also features a character called Killalla of the Glow, who is implied to be one of the first aliens to master the energy later marshaled by the Green Lantern Corps.
  - Heck, she's as-good-as-stated to be one of the Guardians, before the female Oans went their separate way.
- It's never directly stated, but there are enough hints to figure out that Matthew the raven was Matthew Cable, from Alan Moore's series Swamp Thing, before he died. Gaiman owes a lot to Moore in getting his career started; there are several nods in Sandman to Moore's work in the DCU.
A throwaway line in Paul Cornell's Captain Britain refers to Merlin as one of the Higher Evolutionaries, acknowledging the Doctor Who Magazine comic strip's presence in the Marvel Universe for the first time since Alan Moore was writing both characters.
- in one issue of Excalibur Kitty and Rachel are being accosted by Daleks while queuing at a bureaucraticc office
- Plus, Merlin's appearance in Cornell's series looks to be a Call Back to the way he looked in the DWM strip.
Writers and artists often use scenes set in the Batcave's trophy room to give a Continuity Nod to previous Batman stories. Traditionally included are the giant penny from a 1947 fight with The Penny Plunderer, a T-Rex from a 1946 adventure on Dinosaur Island, and a memorial to Jason Todd, first seen in The Dark Knight Returns.
- Also, Batman once investigated murders at a movie set, where the movie being shot was a WWI flying action/drama. The misunderstood Villain Protagonist of said film was Hans von Hammer, in our world the main character of DC Comics Enemy Ace series.
Elf Quest examples:
- In the science-fiction "sequel" The Rebels, Gestrelle Luricahn owning elfin artifacts is just part of her job/field of research. The fact that nearly all of those that we see decorating her room had some importance in previous Elf Quest stories is a Continuity Nod.
- Sometimes panels from earlier comics get "paraphrased", using the same composition and (if possible) characters; for example one in Kings of the Broken Wheel 3 is modeled after one in the very first Elf Quest story ever.
- In a montage of the Wolfriders' dens in Wild Hunt, Tyleet's can be identified by the ornament that her long-dead adoptive son used to wear as a headband.
Quite a few in The League of Extraordinary Gentlemen, which is to be expected as its continuity arguably includes every book ever written.
Asterix does this a few times. In Asterix in Britain, you can see a few souvenirs referring to previous adventures on a shelf in Asterix and Obelix's house (including a model sphinx from Asterix and Cleopatra and a Visigoth helmet from Asterix and the Goths).
Occurs regularly in Astro City, as befitting a series with a single writer. Most Continuity Nods appear as sidelong references to other characters and events in the chronological past/present, even if the subject hasn't had a published appearance yet.
- Samaritan briefly mutters "3.2" when he arrives to visit Steeljack in "The Tarnished Angel." This is a reference to Samaritan's Day in the Life story, "In Dreams," where it's shown he keeps track of how many seconds he spends flying from one scene to another.
- In "Show 'Em All," as Jack-In-The-Box dodges The Junkman's aerosol bombs, he casually mentions having "recent experience" in dodging mid-air explosions. This refers to a single panel from the earlier "Confession" story arc, where Jack-In-The-Box eludes capture from a missile-firing helicopter.
- Also from "Confession", Brian begins his super-hero career by working as a busboy in Bruiser's Bar & Grill, run by retired Golden Age hero The Black Badge. Both the Black Badge and Bruisers' play small but pivotal roles in the later "Dark Ages" story arc.
- Kurt Busiek loves to put Continuity Nods in all of his works, helped by his encyclopedic knowledge of comic book history.
A subtle one from The Amazing Spider-Man vol. 2 #55: Peter Parker, currently working as a teacher at his old high school, talking to the school secretary (or administrator?) who remembers him from when he was a student:

Peter: Good afternoon, Maude. Looking beautiful as always.
Maude: Oh Peter, you lie beautifully darling, have ever since the ninth grade, so don't stop.
Ninth grade was when Peter was about 15, i. e. when he became Spider-Man and had to lie to maintain his secret identity.

In The Beano Annual 2009 the Ratz (a group of rats from a 2000s Beano comic strip) briefly meet the Nibblers (a group of mice from a 1970s/1980s Beano comic strip).