Waving Signs Around

In any mass public gathering, positive (on the campaign trail, during sporting events, to raise awareness) or negative (at protests and/or strikes), there's bound to be people Waving Signs Around.

In more humorous depictions, expect at least one sign to be completely irrelevant to the actual topic--"Hi, Mom", "Buy at Moe's", "I came to this rally and all I got was this stupid sign", etc.

Often accompanied by a Slogan-Yelling Megaphone Guy. See also Torches and Pitchforks, for when the crowd gets too rowdy.

Examples of Waving Signs Around include:

Positive Support

Western Animation

In the Family Guy episode "Mr. Griffin Goes to Washington", there's a guy holding a John 3:16 sign on a baseball game. Brian looks it up, and it turns out that it means: "And the Lord said, 'Go, Sox.'"
In The Simpsons‍'‍ "Stark Raving Dad", the John 3:16 guy turns up to welcome "Michael Jackson" to Evergreen Terrace along with fans with Jackson-specific signs.

Real Life

The John 3:16 guy, aka "Rainbow Man" (owing to his wig).
Monday Night Football - Many of the signs have Fun with Acronyms, using the letters MNF to spell something humorous.
Obama bring back Arrested Development.

Negative Protest Examples

Comic Books

Nextwave is seen carrying protest signs about the Marvel Civil War (and the fact that they're not involved).

Film

Played with in the film version of PCU, where there is an entire student organization evidently devoted to protesting for various causes, the cause in question seemingly changing with each week. At the end of the movie, the protagonists stage a large ad hoc protest against the college president, and offer some of their signs to the leader of the student protest organization, to which they reply "We brought our own" and produce a set of blank picket signs and markers that they evidently carry around with them.
Red October: ALL POWER TO THE SOVIETS! OVERTHROW THE AUTOCRACY! STOP THE WAR!

Literature

In one Hardy Boys story, the boys and their friend (Chester, I think his name was) are investigating a massive protest against a boat, and get handed signs (which makes for a difficult moment when the boys' employer turns out to be the owner of the boat). Chester brings his own sign reading "FRANK HARDY FOR MAYOR".
In Larry Niven's short story "Cloak of Anarchy", one character joins a protest group and holds up a blank sign. He intends this as a sociological experiment to see what people read into the sign; the protesters see him as mocking them and their cause—as they make painfully clear to him when a hacker crashes all the police robots.

Live-Action TV

Father Ted and Dougal protesting outside a cinema (see the Moral Guardians page image). "Down with this sort of thing!" "Careful now!"
How I Met Your Mother - Ted has to wrestle with a crowd of protesters who don't want the Arcadia, a beloved old building, to be torn down.
In Bewitched, Samantha and her Aunt Clara, along with Clara's friends Bertha and Mary, are pissed off at a Halloween candymaker's insistence on a stereotypical ugly old crone for his mascot. They prepare to stage a protest in his home. Their signs read Brinkman Unfair to Witches, Witches are People Too, but absent-minded Clara, reminded she needs a sign, zaps up the first thing she thinks of: Vote for Coolidge.

Newspaper Comics

One Far Side cartoon depicted a protest by the Imbeciles Of America, whose signs were of course crudely made, misspelled, held upside down, etc.

Video Games

Team Fortress 2: The Smissmass update comic has an angry civilian with the sign "RED & BLU OUT OF TEUFORT" as part of a Funny Background Event.
- There is also a melee item called the Conscientious Objector that now allows players to wave signs around...and also kill each other with them.
Goat Simulator has a group of humans in Goatville attending a rally and waving "No penis-shaped food!" signs.
City of Heroes and City of Villains had an emote which let your character wave one of several somewhat incomprehensible protest signs around, randomly chosen by the engine. The same emote was used for groups of protesters occasionally found in Praetoria.

Web Comics

A demonstration in Bad Machinery featured this with, as pictured above, rather polite signs reading "FLIPPING KROPOTKIN" and "COME ON NOW".
In one Xkcd strip, an audience member at a politician's speech holds up the sign " [citation needed] ". Another strip talks about showing up with "contented" signs at rallies. ("THINGS ARE PRETTY OKAY!")

Western Animation

Played with in an episode of The Boondocks. Huey assembles an army of sign wavers to try and shut down Jasmine's lemonade stand, but when Huey tries to start a riot, they just stand around swaying ineffectually. One of them explains that they will shut down the lemonade stand...even if it takes several years.
On South Park the boys get roped into an anti-war protest rally, complete with signs (They only did it to get out of class.) They demonstrate on TV that they don't know anything about it, pissing off Mr. Garrison.

Newsperson: Can you tell me why you marched out of school today?
Stan: Uh.....war.
Newsperson: Right and what about the war?
Kyle: It's, it's....gay?
Newsperson: Uh huh and what aspect of it do you think it most gay?
Kyle: Uh...reading the sign he's carrying no blood for oil!
Stan: Yeah, reading war is not my voice:
Cartman: reading Bush is a nayzzi!

One episode of Johnny Bravo started off with Johnny at a war protest. He was yelling, "I love pie! I love pie!", and holding a sign saying as much.
An example from The Simpsons—in "Itchy and Scratchy and Marge", Marge's anti-Itchy and Scratchy protest, triggered by Maggie whacking Homer in the head with a mallet after she watched one of the cartoons, starts with Marge and the other family members marching outside the show's production company. Homer's sign is a detailed explanation of what happened to him and Maggie's says "Stop Me Before I Kill Again". Bart changes his sign to "Don't Ban Itchy and Scratchy". As the protest grows, additional signs include "Bring Back Wagon Train" and "What If A Mouse Blew Up A Cat And Nobody Cared".
Happened in Futurama with Leela and a group of protesters protesting against a Dark Matter oil rig flying too close to a penguin preserve on Pluto. The sign messages included:

Give A Hooto, Don't Pollute Pluto!
Preserve Our Useless Wasteland
Free Chilly Willy
Protester: (excitedly) Here they come. Oh, I hope they read my sign! (Holds up sign saying, "Go Away Tanker!")

Real Life

Some candidates took to using the national costume competition at the 2020 Miss Universe to voice their grievances towards sociopolitical issues such as anti-Asian hate crimes, LGBTQ+ rights and the 2021 Myanmar protests by either incorporating messages in their costumes, or in the case of Miss Myanmar Thuzar Wint Lwin, holding a rather modest placard calling on people to pray for Myanmar as things have become chaotic in the country, no thanks to its military junta.
The Westboro Baptist Church gained a reputation for picketing of military funerals and anything they can blame on homosexuality as well as other things they see as decadent or gravely sinful, with the infamous "GOD HATES FAGS" sign. Inevitably, some would counter-protest either to directly satirise the "church" e.g. "GOD HATES FIGS" as a play on God's contempt towards figs, or just piss off the Westboro members for the heck of it, like when a counter-protester waved a "Germany for the World Cup!" sign.