There's one right on the film's poster itself◊: those who will remain loyal to Miguel are on the left while those who will rebel to join Miles are on the right.
The film's opening recap/Previously on… segment with Gwen giving a short recounting of the events of Into the Spider-Verse has a few shots of upcoming scenes from the film itself, lacking context, but still containing thematic relevance to her voiceover, such as Captain Stacy trying to arrest Gwen when she says that Miles isn't the only one who "hasn't had it easy" and Miles' betrayed reactions towards Gwen once the truth about Canon Events and his anomalous existence as Spider-Man is revealed to him, as Gwen brokenly says she "didn't want to hurt him". Gwen's dialogue also hints at the film's ending, with her repeated line "And he's not the only one" foreshadowing that Miles will meet another version of himself, and her line about how she thought she "knew the rest but (she) didn't" referring to how Gwen learns that Canon Events can be averted without the destruction of a dimension from her father quitting the force. Likewise, her first lines about "doing things differently this time" set up Gwen's new stance at the film's ending and decision to turn against the Spider-Society and its views with her own allies. Turns out this is actually the speech she's using to recruit people.
When Gwen meets Jessica, she's extremely impressed, and asks if Jess can adopt her. Soon after, Jess becomes a mentor and mother-figure to Gwen.
In the first film, upon being rescued by Peter Parker and their spider-senses reacting to each other, Miles' spider-sense was initially colored in green and purple, the Prowler's traditional comic book colors, before transitioning to Spider-Man's traditional red and blue coloration, symbolizing how their meeting was pushing Miles into embracing a more heroic role in opposition to his villainous Uncle's. The very end of this film has Miles restrained and confronted by an alternative universe version of himself who became The Prowler, apparently as a result of never having met Spider-Man and being driven by Jefferson's death.
Miles ponders that "maybe in another universe," he tells his parents that he's Spider-Man. In the end of the movie, he finally decides to tell his mother that he is Spider-Man... and only when she's confused about what he's talking about does Miles realize that he's not in his home universe.
Also in said film, upon discovering his powers for the first time and realizing that he'd become similar to Spider-Man from a comic book retelling of his adventures, Miles questioned how it was possible for one world to have two "native" Spider-Men in it. Along with the glitching effect on the Spider that bit him, this hinted that said spider was not native to his reality and altered by the Super Collider experiments, but a spider from an entirely different reality altogether. The events occurring to Miles being almost beat-for-beat what happened to Peter Parker upon discovering his powers also hinted at the Canon Events that occur in each reality being apparently fixed predetermined events that always occur regardless of circumstances or foreknowledge of what's going to happen. Miles getting the spider-bite effectively "stole" a Canon Event from a different universe and made him a multiverse temporal anomaly, which fuels Miguel's animosity towards him.
After his initial fumbling with stealing from the ATM, Spot manages to get the bat out of the shop keep's hands, (accidentally) hit him with it, and trap him in a hole. While trying to justify his theft, Spot places cans from a nearby shelf on the ground and uses them to roll the machine out. This shows that Spot is mostly harmless due to inexperience and he will become genuinely effective with the chance to think and learn.
When doing his recap of events during the Time Skip, Miles' sketchbook shows a brief montage of him fighting various supervillians, beating them all one by one with the same punch before a Smash Cut back to his currently ongoing fight with Spot has the same blow being redirected into his face by his adversary's portals. This symbolizes how treating the Spot the same as every other Villain of the Week and an easily-resolvable fight rebounds on Miles by the film's end, as Spot becomes incensed at the disrespect and starts increasing his powers to make Miles treat him more seriously, along with aiming to hurt him in a very personal manner.
The Spider-Sense reverb from the first film occurs between Miles and Spider-Byte, and is noticeably the only instance that this happens between Miles and another member of the Spider-Society. This hints at her defection to Gwen's team after Miguel exiles her in the film's ending.
In the Morales family's meeting with the guidance counselor, the counselor keeps trying to spin a narrative for Miles' life and the direction he wants it to go in. She is constantly annoyed by the interruptions that derail from it, until finally Miles gives her something concrete, to which she says they now need to "stick with the script" - at which point Miles and Jefferson immediately need to attend to the Spot. This sets up Miles' conflict with everyone else for the rest of the movie, where Miles finds himself unable and/or unwilling to conform to whatever path other people keep trying to set for him.
There are a number of hints that Miles is being specifically excluded from the Spider Society for an unstated reason before it's revealed that he too is considered an "anomaly" like the villains they target.
When Jessica Drew is trying convince Miguel to let Gwen join the Spider Society after seeing her performance against Vulture in the prologue, Miguel is vocally against the idea, meaningfully telling Drew that "[she] knows why" when asked for a reason. It turns out to be not an issue with Gwen herself, but her close relationship with Miles that sours Miguel against her.
When Gwen is web-swinging with Miles around the city and catching him up on how things have been for her in the society, she apologizes for not seeing him sooner, making up an obvious excuse that they're extremely strict about where she can visit. This not only foreshadows that everybody from the Society is forbidden to visit Miles specifically, but that Gwen is supposed to be dealing with an anomalous villain in the Spot rather than taking the opportunity to see Miles behind Miguel's back.
When Gwen tells Miles about the Spider-Society, he asks how he can join but an uncomfortable looking Gwen explains it's a small, selective team. However, upon seeing how truly massive the organization is, Miles quips about Gwen's earlier statement, with her hastily replying that many of them are part-time. It turns out that Gwen was lying to Miles — he was never meant to be part of the team.
Furthered by the fact that even before we see how big the Society is, we learn a LEGO Spider-Man, who is logically weaker than all the other Spider-Heroes (having Super-Strength relative to other minifigures) and definitely smaller than the rest, is in it.
When Pavitr first meets Miles in the Mumbattan dimension, Pavitr keeps calling Miles "new guy" despite how he's been his dimension's Spider-Man for only six months, as Miles (who's been Spider-Man for over a year) points out. It turns out to be a deliberate action — Miguel and those in the know in the Spider-Society purposefully didn't offer Miles a spot because of him being an apparent "anomaly".
When first meeting Hobie in the Mumbattan Super-Collider room, Hobie quickly recognizes Miles on sight, calling him "big-under from 1610". At first it seems to be because of his close friendship with Gwen and the stories she's told him about Miles, but it actually means that Miles has a special designation within the society that all its members are aware of but him. Hobie later calls Gwen out for keeping Miles in the dark as they're en route to meet Miguel, saying she should have told Miles his "place in all this". As it turns out, Miguel counts Miles not just as an anomaly, but the original one, as the spider that bit him was from a different dimension, and thus receiving the bite instead of that universe's "Native" Spider-Man means Miles effectively stole a Canon Event and role that was destined for another.
In Hobie's introduction, he says people who call themselves heroes are "Self-mythologizing narcissistic autocrats." This hints at his contempt for the Spider Society and its less-than-savory practices. In addition, it's a fairly accurate and damning indictment of the Spider Society - they are indeed narcissistic in how they ignore the pain of Canon Events, and the whole concept of Canon Events is self-mythologizing.
The Spider-Society only gives Miles a day pass to stop him from glitching. The only other person with a day pass is Mayday, Peter B.'s toddler daughter; Peter B. even says he "didn't know they made that for adults."
When Miguel says "That's why anomalies are so dangerous," his gesture and way that he emphasizes "anomalies" indicates that he is referring to Miles specifically. After he says this, we see everyone in the room behind Miles, looking at him, implying that they too know that he is an anomaly, which Peter B. and Gwen later confirm to Miles.
Hobie Brown a.k.a. Spider-Punk gives a number of important plot points:
He briefly asks Gwen if Miles knows why he's at the Spider Society, with Gwen avoiding the conversation. It turns out Miles was not meant to be part of the Society and Hobie is against the whole thing.
When Miles complains about not having his own watch, Hobie tells him to "make [his] own". While one can think of this as just a Deadpan Snarker moment, the truth is he was being completely genuine with his suggestion. Later in the film he's seen silently robbing tech from Miguel's lab, all of these events ultimately building up to the reveal that he had been crafting his own bootleg watches and gave one to Gwen, thus allowing her to bring back the Spider-Gang even if they don't have access to the actual Spider-Society watches.
When first meeting Miles, Hobie swiftly breaks through a force field the latter was taking awhile to try and pierce with his bio-electricity. Hobie off-handedly mentions Miles should "use [his] whole hands, not just [his] fingertips". This later proves important when Miles is trapped in a Spider-Society force field, and Hobie spreads his palms out to remind Miles how he can beat a force field.
His very specifically sarcastic remark about the Go Home machine is dripping with contempt over how it said to be "ethical" that seems relatively out-of-character for his relatively indifferent persona he carries, almost spelling out to Miles right away that the Spider-Society is not what it seems at first glance and to warn him about the trap he's walking into.
Everything about Spider-Punk screams "Anarchist who is a lone-wolf". Miles even notes that he doesn't seem like he'd fit into a rock and roll band since that's an organization. He's also clearly disdainful of Miguel. When Miguel traps Miles in a force-field to stop him from being able to get home to save his father, Spider-Punk reminds him of the advice he gave him earlier about breaking force fields, allowing Miles to break free. Pleased to see Miles escape, Spider-Punk immediately quits the team and returns back to his universe while every other Spider-Person proceeds to try to recapture Miles.
Hobie is notably a bit of a nuisance from the moment the group returns to the Spider-Society, and initially one might get the impression him showing Miles how to free himself before quitting is just him trying to create anarchy for anarchy's sake. However, at the same time he had no issue with being a proper Spider-Man when the situation called for it in Mumbattan... all of which foreshadows that a lot of his actions are actually Obfuscating Stupidity to hide that not only do his problems with the Society go deeper than just a dislike of authority, but also that he's much, much more competent at subverting it than he appears.
Lyla calls Gwen when the latter is in Mumbattan to warn her about a "canon" event and that she should stay clear of it. A minute later, Gwen tries to stop Miles from saving Inspector Singh out of apparent concern for his safety. While this concern is genuine, Gwen also meant to prevent Miles from disrupting the "canon" of the Inspector's death, as according to Miguel's theory if messed with, can cause universal damage.
Although it's disappointing and heartbreaking to see Gwen accept the Spider Society's indoctrination and betray Miles, it's equally awesome and heartwarming to see her progress away from it.
When Miles disrupts Pavitr's canon event, Gwen is worried, yet also sincerely tells Miles she 'always' thinks he's 'amazing'. She's starting to realise there's more to being Spider-Man than preserving canon.
Next, while chasing Miles, Jessica tells Gwen, 'I know he's your friend, but it's the only way', and Gwen responds 'But my gut says...' before Jessica overrides her.
And after Miles calls her and Peter out for knowing he was an anomaly, shunning him, and never telling him - and then tells her, 'Goodbye Gwen', she looks utterly broken. Then Miles shocks Miguel and breaks away, and she initially calls after him out of concern. But once she sees Miles has successfully escaped, she smiles. That just might be the point where Gwen stopped betraying Miles, and started being there for him again (even if he doesn't realise it yet).
Cemented when she throws her armour-piercing line at Miguel: 'We are supposed to be the good guys', when Captain Stacy quits and she realizes breaking canon won't destroy her universe, and when she tells Miles's parents how much Miles loves them, and promises she'll find him.
The Spot's vision of the future shows Miles's father coming to the rescue of a child before being crushed to death by debris. The scene has Jefferson be swapped out with Captain Singh in some frames, not only foreshadowing Singh's own near-death, but the idea of a Spider-Man failing to save a Captain being a Canon Event and a universal constant.
Whilst fleeing from the entire Spider-Society during the climactic chase sequence, despite having honed his invisibility to the point that he was able to spy on Gwen in the same room for an extended period without her detecting him, Miles does not use that power to aid in his escape from his pursuers, only using his agility and web-swinging to just barely keep ahead of everybody. As he reveals to Miguel during their close-quarters grapple atop the bullet train, this was because he wanted everybody to chase after a moving but still visible target, luring the entire Society out of their headquarters and giving himself a window of opportunity to use the multiverse travel technology within unimpeded to reach his home universe. Miles also shoots a pointed look at the Spider-Society building as he's rising atop the city on the bullet train before Miguel catches up to him, likely judging if he's managed to lure them all far enough away from the place before he can turn back.
Miles initially tried to break through the force field at Alchemex on Earth-50101 by "absorbing the power and sending it back", to which Hobie advises he use his whole hands next time. When he confronts Miguel on the space elevator, he uses his whole hands to absorb the power from his holographic Spider-Suit and send it back, rocketing Miguel to the back of the train and freeing himself to pursue his true Batman Gambit.
While Miles is on Earth-42, when that universe's Rio walks in the room, Miles hastily puts on the coat and shirt he's been wearing earlier in the film. Only this time, they are purple and green instead of red and blue, foreshadowing that Earth-42's Miles is the Prowler.
As mentioned, Donald Glover plays the Prowler. It's also known that Glover is the inspiration for Miles Morales' existence and even plays him in Ultimate Spider-Man. In other words, he's both Spider-Man and the Prowler — just like Miles-1610 and Miles-42, the very character(s) he inspired.
When Miguel is ranting at Miles and revealing his anomalous nature in the Multiverse, he states that Miles will be an anomaly anywhere he goes, not just in Nueva York. Whilst he means that Miles is an anomaly because he received spider powers from a different universe, by the end, this same fact means that Miles starts glitching out in what the Go Home machine believes to be his "home" universe — the Earth-42 his spider came from.
During the Spider-Society sequence, there's the recurring bit about Peter B. being a good or bad mentor to Miles. In the ending, we see what a really, really bad mentor looks like. Just not in the sense Peter B. intended.
When Miles is preparing to reveal his identity to his mom, he repeats a lot of the things Rio told him in her big speech earlier in the film, but Rio just looks completely confused by what he's saying. This is another hint that he's in the wrong universe, because this version of Rio never gave her son that speech and therefore has no idea what Miles is referring to.
Peni Parker has become noticeably more cynical given that she's one of those who tries to convince Miles to let his dad die and her design is more run-down than the previous film but she doesn't take part in the big climatic chase, nor does she guard the "Go Home" machine. Despite having become more run-down, it's not enough to stop her from joining Gwen's group to save Miles.
◊: those who will remain loyal to Miguel are on the left while those who will rebel to join Miles are on the right.
