Does the title of True Detective have any meaning within the show?

Entertainment Weekly explains the origins and the meaning of the title:

True Detective takes its title from the pioneering pulp magazine True Detective, the king of the so-called “Dickbooks,” which launched the true crime category in 1928 at the dawn of the golden age of the pulps, and folded in 1995 after decades of chasing grittier, grimier degrees of “realism,” dead-ending in a gutter of smutty sleaze. But HBO’s True Detective is not homage; the association is ironic. The pulp wallowed in sensationalism; the show, while disturbing, does not. The pulp was “true” in that it profiled real-life crime; the show, all fiction, is concerned with philosophical truth and honesty. The pulp celebrated heroism and made icons out of its villains; the show deconstructs both heroic character and what Joseph Conrad called “the fascination with abomination.”

Rust gets treated poorly by many characters and isn't well liked by other police, largely due to his detached, analytical nature and his contrarian beliefs. In contrast, Marty is seen by others as a friendly family-man and a good cop. However, as the show goes on we start to see more of their true qualities.

Rust actually had a family that he cared for (and still misses based on the call to his ex-wife) that was broken up due to circumstances out of his control. Marty argues constantly with his wife, cheats on her multiple times, and eventually causes his family to fall apart through his own selfish actions. Marty is also prone to impulsive, emotional actions that he often later lies about, where Rust is much more rational and arguably has stronger morals.

The way that Marty presents himself to others is deceitful, but Rust is typically truthful outside of lies necessary for his job, even if other people don't like the truth. Rust's life was severely impacted after he murdered a child abuser, but when Marty does the exact same thing it gets covered up and he's presented as dutiful and courageous. As such, Rust could be seen as being much more true in character in his dedication to truth and righteousness (which also happen to be good qualities for a detective). Even if murder is wrong, both detectives felt it was unacceptable to let those people live; only one was honest and accepted the consequences.

The title could also extend to their actual positions, suggesting that only one of them really deserves to be a detective. Rust seems more knowledgeable and curious than Marty, carries out more of the investigative work, and is even known (and mocked as "the tax man") for his meticulous note taking and examination of evidence. He goes so far as to continue working on the case for years on his own after it's been closed and he leaves his position. He also takes matters into his own hands when there isn't a legal method of proceeding with the case, threatening people or attacking them. While this is unethical, he does it in the pursuit of solving the case where Marty will resort to violence purely out of emotion. In terms of "catching the bad guy", Rust is clearly the True Detective.

I'm going to say yes--to some degree, but to determine what "true" is, may be subjective to our own moral ethical standards...

I think one reason it is called True Detective is because is playing on True Crime.

True crime is a non-fiction literary and film genre in which the author examines an actual crime and details the actions of real people. The crimes most commonly include murder, with tales of serial killers dominating the genre[1] (about 40% in a 2002 survey[2]), but true crime works have also focused on other subjects, for instance policemen memoirs, and more recently reality police TV shows.[1] Depending on the writer, true crime can adhere strictly to well-established facts in journalistic fashion, or can be highly speculative. Some true crime works are "instant books" produced quickly to capitalize on popular demand; these have been described as "more than formulaic" and hyper-conventional.[3] Others may reflect years of thoughtful research and inquiry and may have considerable literary merit.[2] Still others revisit historic crimes (or alleged crimes) and propose solutions, such as books examining political assassinations, well-known unsolved murders, or the deaths of celebrities. Although the genre examines real historical events, true crime TV series typically use reenactments to help draw in viewers.

However, over the years the more traditional view of True Crime being solely non-fiction has somewhat changed and is now used within genres of fiction with stylization (realism, hard boiled), execution (memoir-structure), tone (serious), and themes (us against them/me against the world)...And this matters because the juxtaposition to fictional true crime, then lends itself to the questioning of what is "true-crime" itself?

Fargo (the film and tv series) for instance, is a dark comedy crime drama, and presents itself as story of "True Crime". The reasons for that are both the ideas that is funny to assume that events in real life would ever actually happen this way, as dark comedy lends itself to farcical plots/tropes, but also because Fargo still executes itself in a serious dark crime-drama manner, with it's own characterizations of realism, and does have decent (usually detective/police) characters with integrity, fighting against people whom are often criminally insane. (There are grey characters too, though) However some of the crimes or plots Noah Hawley has used in his TV series, do sometimes come from "real" crime stories in the Dakotas/Minnesota area--so there in fact are elements of real 'true crime'.

True Detective then follows suit in some ways, because it is a dark/gritty FICTIONAL Crime Drama, but it does present a RUSTic-realism reality and is looking more inherently at the nature, behavior, or psychology of people involved in both the crimes and law enforcement, so I would agree with you it is in fact asking, "What IS a true Detective?"

TD's creator has insisted that there is no supernatural phenomenon, but I think by definition a person can still argue that TD, especially the first season, does have magical realism elements, meaning it does at times look like supernatural things are happening, despite that, in this case, there are also "real-world" explanations for all of those things. Magical Realism is also tricky genre to define because you have works like A Hundred Years of Solitude that relies on an unexplained idea that somehow, someone can exist further than a lifetime or something like Mark Helprin's Winter's Tale that is set in a very realistic period-New York City, but is sprinkled with fantasy elements and both are considered magical realism...

(Note: Another example of something similar to True Detective or Fargo borrowing on 'True Crime', might be Longmire, albeit with Native American magical-realism elements sprinkled through a rural-setting, featuring the concept of the dying cowboy and historically unresolved Native American conflicts.--Also Dana Gonzalez is both Longmire's and Fargo's cinematographer)

But one reason True Detective would want to use that genre, was again to home in on examining the nature of these characters and their reality--and decide what or whom is "true" and how "true" can be antiquated with either good or bad and how complicated those ideas really are when we are looking for hope from damaged people. Both main characters, Rust and Marty each have their own problems and those problems affect how they investigate, but argumentively I think the series tries to make the case that as flawed as they are, they're still pitted up against something that comes across as something more evil, then their own predispositions. And I think the same case can be made for second season characters, despite I feel like it's somewhat philosophically opposite/challenged to the ideas the first season purposed in Rustian philosophy....

We're talking cop talk here. The concept of a true detective or a "real detective" (read Michael Connelly's books or watch Bosch for this alternate phrasing) is someone who relentlessly pursues the case, follows the trail wherever it leads, perhaps forsaking other duties outside of the job, and attempts to solve the crime for every victim, regardless of status, as opposed to just anyone wearing a detective's shield collecting an arrest for the clearance rate. The pulp magazine title honors the true detective hero.