You might be asking why TV Tropes has an article about trademarks (and servicemarks). Well, so that you can understand what they are; what they aren't; how someone else (other than the mark's owner) is allowed to use them in a story; when they can't (or their lawyer thinks they can't) use it; under what circumstances someone using them as part of a media franchise can get a trademark; and when they can't. This will also let you understand why sometimes they use an obvious fake name in place of an (even more obvious) brand name.
Trademarks (and service marks; that term will be explained later) are a term used to refer to an identifier for something placed in (legal) commerce. We have to make this additional point about it being legal, because you can't get a registration for something illegal. If, for example, you developed an improved version of crystal meth, that's bright blue because of its high quality, you won't be able to get a trademark registration on whatever name you put on it (or possibly on the color, as we explain below) because the product isn't legal, or more likely, the cops will get your address from the trademark application and come bust you.
If one applies for a trademark/servicemark registration and it is granted, it gives the mark's owner a considerable amount of protection. They can stop the importation into the country of counterfeit goods carrying that mark, stop others using the same or deceptively similar mark, and, just like with bootleg copyrighted material, they can get a court to order the "impounding" (Federal marshals and/or FBI or Treasury Department officials can seize) of knockoffs, and if proven to be knockoffs, destruction.
Trademarks are statutory in nature, meaning that in some cases you might have a perfectly valid and unique name but the law may prohibit you from registering the mark or claiming an exclusive right to an unregistered mark. For example, you can no longer claim exclusivity on a location as part of a mark, but you can if you had a mark registered before about 1990. Someone at The Washington Post failed to notice its trademark for the name of the paper, held for over 100 years, had expired. Had they kept it registered, under the old rules they would still have an exclusive right to the name Washington as part of the mark, but now they have to disclaim an exclusive right to the name of the city as part of the mark when they re-registered it. Remember this, I'll come back to it later.
Also, a trademark/servicemark can't be "offensive", e.g. a woman registered a word for lollypops in the shape of a rooster. If you guessed the word she used was "cocksuckers" you can probably understand why her registration was cancelled. Also, there have been attempts to cancel the Washington Redskins mark for its football team because it's considered offensive to Native Americans but a previous attempt was overturned in court on technical grounds, basically the mark has been in use since the 1940s and registered since 1967, so if there were objections they're supposed to be filed before the mark has been registered for twenty years.
Trademarks and Servicemarks come in two flavors: registered marks and unregistered marks. In some jurisdictions, ownership of a mark comes from registration, if you don't register the mark and someone else does, they own it. (This is the situation with Internet domain names.) In some jurisdictions, the first party to use a mark owns it, and can take away ownership from someone who started using it later even though the other party had registered their use of the mark and the first user did not. (This is the status in the United States.) There are, of course, various exceptions to the rules, which is why we say that the wives of lawyers that handle this sort of law have mink coats. To add to the fun, a trademark/servicemark can be registered with the U.S. Patent and Trademark Office, or it can be registered with the Secretary of State or equivalent agency in each state where the goods or services are sold. Or it can be registered at both the state and federal level. There are two reasons for this: if you only operate in one state, a state registration may be enough to start, is generally cheaper (about $50 or less vs. about $300) requires less paperwork (often nothing more than one page and a copy of the item or the advertising) and if you get to the point that you want to register the mark federally, the state registration can serve as evidence of the first use of the mark, which can be helpful if someone else uses the same or a similar mark to yours and you need to show you used it before them. Also, it gives your lawyer an option, in which they can sue in either federal court or state court, which, may be more advantageous in some cases.
Also, if you register a domain name and someone else claims they are entitled to that name, the domain dispute process looks to see if either party has a trademark or service mark registered at the national level of some country, so state-level registrations don't count. Due to the much faster processes involved, some companies that don't even operate there are registering marks in the country of Tunisia (and then take advantage of the Madrid system for their trademarks to have validity in several countries of the world).
Generally, if a mark is not registered, the owner will try to warn people it claims some ownership by using TM next to the term. If a mark is registered with the Federal Government through the Patent and Trademark office, the owner can use the R-in-a-circle ® symbol, or the much older "Reg. U.S. Pat. & TM Off." (Dupont likes to use the old format on its corporate logo). You can't use the ® on a mark only registered at the state level, but you can mention the state registration, e.g. "Trademark Registered with the Virginia Corporation Commission", "Servicemark Registered with the Arizona Secretary of State." etc. A lot of companies would register their marks with the Pennsylvania Department of Agriculture, which is why a lot of products would have a notice "Reg. Penna Dept. of Agr." on them. Some countries did not allow the use of the R in a circle notice so some countries where a product's mark is registered the product would have the notice "Trade Mark Regd." on it.
There are certain marks you cannot register. This varies by country, but here are some examples from the United States. A mark consisting of the coat of arms of seal of a country generally isn't registrable. Also, a government may grant trademark status for certain terms used by its organizations, these are called "Chartered Marks" because the ownership of the mark was granted by charter. In the US, The Boy Scouts, the 4H Club (and its special 4 leaf clover), the FDIC, and certain other organizations, have been granted ownership of their name or mark by statute. Also, the state flag and state seal of each of the 50 states is not registrable by a private organization.
As a result of treaties between countries, there are marks of international organizations that can't be used without their permission (unless you were using the mark for something before the mark was granted treaty status). The word "Olympic" or the 5 interlocking rings; the United Nations flag or logo; The Red Cross (Johnson & Johnson can still use the Red Cross for cotton in the United States because they were using it more than 100 years ago before the symbol was protected), Red Crescent (some Muslim countries) or Red Crystal. (The Red Crystal got created because the Arab countries wouldn't put up with the use of a red Star of David as the Israeli Red Cross used, so they picked something less offensive.)
But even then, the restriction is only with respect to goods or services using a protected name or symbol; if you're making a movie involving a UN peacekeeping agency, you can put UN uniforms on the actors and use the UN flag or logo on their vehicles, or film a scene where International Red Cross workers are involved because of the First Amendment. As long as you don't try to include the protected symbols or names in the advertising for the movie, it's unlikely a court would prevent you from doing so unless you tried to claim you had approval of the organization. Although if the usage puts them in a bad light, they may threaten litigation. (See below about "disparagement.") The Metropolitan Washington Airports Authority made noises that they were going to take legal action against Die Hard 2 because of its frequent mention of "Dulles Airport," which it operates, but nothing happened, someone probably realized they have no grounds to sue and would simply provide lots more publicity, vis-a-vis the Streisand Effect.
So anyway, a trademark is an identifier. That identifier can be a word or two (Perrier water, Total gasoline, Microsoft software, Jiffy Lube oil changes), a phrase (The Sweetheart of the Corn is a trademark that still appears on boxes of Kellogg's Corn Flakes, and Canadian Club Whiskey is also known by the phrase The Best in the House), an image (called a 'device' in trademark law) such as the Bat symbol (not to be confused with another bat symbol) appearing on a bottle of Bacardi Rum, a color (Owens Corning won the right to trademark the color pink for use in fiberglass insulation), a layout design (The design of the label on a bottle of Jack Daniels is the property of the Jack Daniels Distillery, as they will be happy to inform you if you use it without permission), or a sound (The MGM Lion's roar for motion pictures). The latter are technically referred to as trade dress, as a "mark" is specifically a phrase or image used to mark an item to denote its manufacturer, but share similar protections.
Trademarks are proper names; that's why they are capitalized when used to refer to the particular product or service. A trademark is classed as "strong" or "weak." A strong mark is so significant that any use typically implies the original company, e.g. if you sold silverware with the name "Exxon", Exxon Mobil would very likely be able to successfully argue in court that anything with that name would be thought to come from the oil company. However, if you sold something under the name "Acme", that mark is so weak that even Warner Bros. probably couldn't stop you.
The reason for the strong vs. weak dichotomy is that if you have a registered mark or use an unregistered one, you can't necessarily stop someone else from using the same or a similar mark on completely different goods or services unless your mark is considered "strong". Going back to Exxon Mobil again, they had a bit of trouble with Kellogs. Now, Kellogs sells Frosted Flakes cereal with their mascot, Tony the Tiger. At some point after this, Standard Oil of Mew Jersey (the predecessor to Exxon) started advertising Esso gasoline along with a tiger, either real or a drawing. Kellogs didn't have a problem with this; gasoline has nothing to do with breakfast cereal or food. Flash forward forty plus years, and what is now Exxon Mobil wants to sell food at some of its gas stations under the "On The Run" name, and use their unnamed tiger mascot. This, however, Kellogs was not happy about, and won in court to stop Exxon Mobil from using a tiger in connection with the sale of food. Again, Kellogs specifically told the court it had no objection to Exxon Mobil using a tiger image at their gas pumps or in connection with the sale of gasoline.
Trademarks encompass two types of identifiers; a "trademark" is an identifier applied to some physical thing (a "good"). A "service mark" (or "servicemark") is an identifier applied to some practice (a "service") that is made available to the public but doesn't actually provide some physical thing. For example, your house has electricity for power and may have natural gas or oil for heating. The brand the electric company uses (PEPCO is the electric company for Washington, D.C.) is a service mark because you don't have any actual goods (you can't store electricity). However, the brand of oil or gas is a product you do receive, a physical good (which you could store), and is a trade mark. If you receive gas from a particular company (Wisconsin Gas Company) that does not use a separate name for their gas, then the company's name can be a trademark. If you received oil from a delivery company, that can be a servicemark as well as a separate trademark on the oil by the company that refined it. Now, if you are supplied utilities by a company that provides both gas and electric (the Pacific Gas & Electric Company of San Francisco) then their name can be both a trademark and a service mark. The term "wordmark" is also seen - this indicates a specific logo that consists of the word written in a specific font, color and spacing rather than a contrived device.
Now, if you're going to use a mark for a product or as the name of an organization (like a band), if it's the same as someone else's name or mark (because you are doing a homage) the original owner may not like it and can probably demand it be changed. During the 1960s, two groups named themselves after other organizations. Pacific Gas and Electric did not impress the San Francisco-based public utility, so it changed its name to PG&E. Another rock group used the name of the local bus and rail transportation company, the Chicago Transit Authority. They also did not like this, so the band changed its name to Chicago.
Now if you've been paying attention, what problem does the group Chicago have with their name? Remember the example I gave earlier about The Washington Post failing to renew its mark, and now cannot have the exclusive right to its city in its name? The group Chicago registered its mark back when you could. If the group Chicago ever fails to renew its trademark, they will lose the ownership of their name.
In the examples given earlier, the color pink used on insulation is a trademark (you actually have the insulation), but Jiffy Lube is a service mark, you had the service of an oil change done (and the oil change is done using oil bearing the "Pennzoil" trademark). As noted earlier, in some cases the identifier can be both a trademark and a servicemark. While the MGM Lion Roar sound was a service mark until the 1980s since you didn't get a copy of the film, you just got the service of viewing the film, but now you can get the service of watching a film (in a theatre, via pay-per-view or on-demand via cable or satellite, or on-line via streaming), and the goods of the actual film (on video disc, or digital download), this sound mark could be both a trademark and a service mark.
A trademark or servicemark is used to identify goods or services that you produce; you do not necessarily have to be a commercial organization or even making a profit to obtain one to identify your products and services. For example, a religious organization might have a trademark on the name of its particular religious text ("The Most High Sun Prayer Guide") and a service mark for the name of its particular religion. ("PraySun"). This is exactly the situation with the Church of Scientology, where "Scientology," the name of their religion, is a registered servicemark, while their primary reference manual, "Dianetics" is a registered trademark. The Salvation Army has a service mark registration on its red shield, and the Jehovah's Witnesses have trademarks in their publications "Awake!" and "The Watchtower". The United States Department of Defense has a service mark in "American Forces Network," its broadcasting/satellite TV arm for members of the military even though its stations do not run commercials.
There's also a third class of trademark/service mark where the mark's owner licenses use of the mark to third parties. For a commercial business, it's called franchising. McDonald's, Burger King, Wendy's, etc. own their own restaurants and also franchise use of their trademarks and service marks to others. However, when you do not use the mark yourself but allow third parties to use it to certify that the goods or services they sell meet certain quality requirements, then it's a "certification mark". Some examinations for various professional certifications such as advanced insurance agent, software programmer or accountant are examples. The UL label on products indicates that the manufacturer submitted its device to Underwriters Laboratories Inc. for destructive testing; if the device survives over what would be extreme use by consumers, the manufacturer gets permission to put the UL certification mark on its product.
A trademark or service mark can be valuable for those who sell products directly (e.g., Ore-Ida as a brand of french fries) or who sell through franchisees who purchase the permission to use that trademark (e.g., McDonald's as a brand of french fries).
Trademarks, along with Copyright and patent, are considered "intellectual property" in that it's a special type of government-granted monopoly. Trademarks, however are different from copyright; A copyright owner can ignore some infringing uses of its works and does not lose the ability to go after other infringements. But if you own a trademark and do not make efforts to stop unauthorized uses of your mark of which you are aware, someone doing exactly that can use your failure to "police" your mark to prevent you from stopping him from using it as well - this aspect of trademark is sometimes referred to as defend or die. It's why the International Olympic Committee, the NFL, etc. seem to be absolutely tyrannical with regard to their trademarks - the law pretty much demands they have to be. (Yes, they're quite aware of the "damned if they do, damned if they don't" position they're in. Cease-and-desist letters for non-malicious infringement often take on an apologetic tone, thanking the person for their support but explaining why they have to tell them to stop, and these sometimes go viral.)
Also, if a trademark does not represent a distinct, specific owner to people who use the product or service it identifies (as opposed to the trademark or service mark being the "generic" term used to describe the product), the trademark can be declared "generic" by a court and then anyone can use it. This is why anyone can call acetysalicitic acid "aspirin" in the United States, it's become the generic term for that product. (Aspirin is still a trademark of Bayer in the United Kingdom, however.) This is why Johnson & Johnson (creators of Band-Aid bandages) and Xerox tried to discourage the public from using their trademarks as generic terms for the type of productnote —it weakened the respective trademarks.
There's another issue about trademarks, generally for titles of works of art like books, films, songs, you can't register the title as a trademark unless the work is extremely popular or has a very long history of use. Harry Potter or Left Behind as the title of a series of works could be registered, but probably not the titles of the individual books in the series. This can cause problems because there are two completely unrelated movies named Crash, one about people that set up car crashes as erotica, and another that won an Academy Award. But, if you have a particular work and someone else releases something under the same or a very similar name you may be able to stop them. But there are exceptions, especially for parody. This is why porn movies usually do puns that are similar to mainstream movies ("Juranal Park" for Jurassic Park, "Saturday Night Beaver" for Saturday Night Fever and "Schindler's Fist" for Schindler's List) as it can be considered parody, which comes (no pun intended) under Fair Use, below. There are exceptions; there is both a clean film called "What's Love Got To Do With It" and a porno film of the same name. How come the porno is able to have the same name? They used it first.
Then there is the concept of Fair Use, (which while normally relevant to copyright, also applies to use of other people's trademarks), where someone can use someone else's trademark whether its owner likes it or not. For example, let's say I run a blog and I post openly that I happen to hate Coca-Cola because I think it tastes bad, and I happen to like Dr. Pepper. They can't successfully sue me because it's a legitimate commentary. (To be fair, I will note that my brother, on the other hand, likes Coke and hates Dr. Pepper.) This use of their trademarks is fair use because I am giving a comparison of products. Besides that, it's pure opinion; there is no objective way to prove if a soft drink tastes good or bad. Now, if I sold a soft drink called "Swill", and I ran a survey, I could legally say that "86% of customers preferred Swill over Mountain. Dew" (as long as it was true). (This was the entire premise of the Pepsi Challenge, where Pepsi showed that people preferred it over Coke, and started the Cola Wars of the 1980s.)
But you have to be careful, especially in advertisements. Taco Bell got into a public relations disaster after - without asking him first - they ran ads suggesting rap music performer 50 Cent (Curtis Jackson) change his name to 79 Cent, 89 Cent, or 99 Cent, and order one of their menu items at that price, and they'd donate $10,000 to the charity of his choice. He sued them, and it's probably likely the settlement Taco Bell agreed to was considerably more than $10,000, and probably went to his pockets directly.
Now, however, the movie "Inside Man" has a kid playing a violent video game, explaining how he likes it. 'It's like my man 50 Cent says, "Get rich or die tryin'"' This use is merely conversational, does not imply Mr. Jackson approved of the use of his trademark - yes, he has actually registered "50 Cent" as a trademark - and thus the use in the movie is legal as fair use even without his permission.
Famous people registering their name or nom de plume as a trademark or service mark is not that unusual. Frank Sinatra and Stephen Hawking have done so; the Estate of Marilyn Monroe has both that nom de plume and her birth name, "Norma Jean Baker" registered, Which name the Estate of Elvis Presley has registered is left as an exercise for the reader.
However, there is the issue of "disparagement," which means you claim something about a company, product, or service which makes it look bad. If it's pure opinion, such as my example from above how I dislike the taste of Coke, there's nothing they can do about it. If the statement is true, they also can't do anything (on YouTube you can find the video of a New York City Kentucky Fried Chicken - Taco Bell restaurant at 6th Avenue and 4th Street in Greenwich Village where rats were running rampant.) But, if the statement is factual, and false, then that is actionable. To pick on the Coca-Cola Company again, let's say I do a blog, where not only do I say their flagship product tastes like piss, I say it's because they use actual sewer water in the product. Then, since that's clearly untrue, then they can sue, demand a retraction, an apology, and other damages.
This was the case when some Amway dealers were spreading false rumors that an executive of Proctor & Gamble ("P&G", as they've been known for over a hundred years, who makes products that compete with some of Amway's offerings) was a practicing satanist who had gone on TV to admit this (which he hadn't) and that P&G's "man in the moon" logo, that they had used for decades was a satanic symbol (it wasn't). The company successfully sued some of these people, but the damage was so bad P&G had to drop their old logo and create a new one. In this case, P&G was able to sue over these false rumors, but not always. For a disparagement case to be successful, what's said must be untrue and people would have to believe the lie. If I pick on Coke again and say in my blog that it tastes like piss because they use swamp water direct from the planet Mars, that's clearly hyperbole because no one could seriously believe it's possible to import anything from another planet. But if someone says something provably wrong that could be believed and it makes that product look bad, there is a good chance the manufacturer can go after the speaker or publisher for disparagement. (This is also why it's legal to give these fictitious examples about Coca-Cola in this article because it's clear that I am identifying them as false and am not intending that anyone believe them.)
Then there's the problem where a trademark or servicemark is so successful that people use the mark interchangeably with the non-branded name. When a mark becomes generic, anyone can use it, and it is no longer capitalized except when used as the first word of a sentence. Note that a mark can be generic in one use and a strong trademark or service mark in another. It's perfectly legal to sell solid fuel under the name "coke" (a type of processed coal) without getting permission from anyone, but unless you're selling "The Real Thing" you'd better not try to sell any beverage under the name "Coke" unless it's authorized by the Coca-Cola Company of Atlanta. The word "peanuts" (not capitalized) refers to nuts that grow underground note , but the word "Peanuts" (capitalized) refers to a comic strip by Charles Schulz as well as a series of books and TV specials.
The strongest identifiers which can be used as trademarks or service marks are coined words that have no other meaning (Exxon) and use on unrelated products could be stopped, while marks that have been used for a lot of different things may be so weak (Acme) that only a competing use on the exact same product as sold by a third party can be stopped by a trademark owner. And some marks cannot be made trademarks because they are the only way to use that particular term. A company named Blish Manufacturing tried in the 1940s to register as a trademark the word "Copyright" as a brand of flour. The Patent and Trademark Office turned them down because there would be no way for any competing flour manufacturer to put a copyright notice on its product without infringing on Blish's trademark. Conversely, Hasbro has found itself renaming certain characters in its Transformers franchise—packaging doesn't refer to 'Ravage' or 'Ratchet', as those are common English words and thus relatively weak; however, 'Decepticon Ravage' and 'Autobot Ratchet' don't have a lot of other uses unless you're talking about toy robots. (And heaven forbid you see the word 'transform' in the instructions, or it might be the only way to refer to toy robots that change into things ... )
As the above discussion has proven, trademarks are a useful concept, although subject to the same kind of abuses as other intellectual property. However, people see them all the time, and often there seems to be little reason for them. Since they get annoying rather easily, and there is a culture of snark that takes nothing seriously (least of all something like punctuating every sentence with a meaningless TM), we have a prominent trope describing the act of parodying the practices of trademark holders, called Trade Snark.