What's the Difference Between a Killer's Signature and M.O.?

iStock/fergregory
iStock/fergregory

True crime shows, documentaries, and podcasts are everywhere these days, not to mention all the crime-focused movies and TV shows—like NBC's Law & Order: SVU, CBS's CSI: Crime Scene Investigation, and Netflix's Mindhunter. And you've probably heard terms like signature and M.O. being thrown around a lot without much explanation as to what they mean, or how they're different.

If you're confused about the difference between them, well, you’re not alone. As former FBI agent and behavioral analyst John Douglas notes in his book Mindhunter: Inside the FBI's Elite Serial Crime Unit (which the Netflix series is based on), "Both [signature and modus operandi] are extremely important concepts in criminal investigations analysis, and I have spent many hours on witness stands of courtrooms throughout the country trying to get judges and juries to understand the distinction between them."

Douglas, who was recently in New York to promote his new book, The Killer Across the Table: Unlocking the Secrets of Serial Killers and Predators with the FBI's Original Mindhunter, out now, helped break down the difference between signature and M.O. for us.

M.O. stands for Modus Operandi, and, according to Douglas, it's a learned, dynamic behavior. "When a criminal starts perpetrating crimes, if something doesn't go right, he's got to perfect the M.O.," he tells Mental Floss. "He's got to get it better and better." In other words, unless an offender executes the perfect crime his first time out, he'll continue to tweak his M.O. as he goes. The method of committing the crime is modified for success. That's why, Douglas says, "you shouldn't link cases together strictly by modus operandi. … You don't do that because those characteristics could fit people that have nothing to do with the case as well."

But what you can use to link crimes together is an offender's signature, a term that Douglas says he coined. "A signature is a ritual—something [that] is done that is not necessary to perpetrate that particular crime," he says. "The signature is the ritual that is unique to the offender, and that's what you're looking for."

To demonstrate what he means, Douglas uses sports as an example. "It's like a baseball batter [who], before a ball comes in, does rituals," like touching his hat or cleats. "Or shooting a basketball: bounce it three times, [do a certain move], take the shot. It's not necessary to get it in the hoop or hit the ball, but in his mind he's got to do it. He's got to do it this way."

In Mindhunter, Douglas acknowledges that "the differences between M.O. and signature can be subtle." To demonstrate just how subtle, he compares two robbery cases. Both robbers made their captive undress; one "posed them in sexual positions, and took photographs of them" while the other did not take photos.

The latter made his hostages undress "so the eyewitnesses would be so preoccupied and embarrassed that they wouldn't be looking at him and so couldn't make a positive ID later on," Douglas writes. That's an example of M.O. The former robber is an example of a signature, because it wasn't something the offender had to do to rob the bank—and actually put him at risk of being caught, because he was in the bank longer. "It was something he clearly felt a need to do," Douglas writes.

Because the signature is unique to the offender, Douglas says that you can use it in trials: "A case in Washington state, the subject was posing the victims after he killed [them]. And all that was allowed for me to testify to."

There's one challenge with signatures, though. "You can only see it when it starts showing up in repetitive crimes," Douglas says. "You can't look at a single case and say, 'Oh, this was the signature.' Say the victim is posed—that may end up being the signature, but you've got to compare it to something, later on."

As criminology professor Scott A. Bonn, Ph.D., points out in a post for Psychology Today, "While every crime has an M.O., not all crimes have a signature." Now, whether you're listening to a true crime podcast or watching an episode of Mindhunter, you'll know the difference.

Why Are Barns Often Painted Red?

iStock/Ron and Patty Thomas
iStock/Ron and Patty Thomas

Beginning with the earliest American settlements and continuing into the 18th century, most barns weren't painted at all. Early American barn builders took sun exposure, temperature, moisture, wind, and water drainage patterns into account when placing and building barns, and they seasoned the wood (that is, they reduced the moisture content) accordingly. The right type of wood in the right environment held up fine without any paint.

Toward the end of the 1700s, these old-school methods of barn planning and building fell by the wayside. People sought a quicker, easier fix for preserving their barns—a way to coat and seal the wood to protect it from sunlight and moisture damage. Farmers began making their own coating from a mix of linseed oil (a tawny oil derived from the flax seeds), milk, and lime. It dried quickly and lasted a long time, but it didn't really protect the wood from mold and wasn't quite like the "barn red"we know today—it was more of a burnt orange, really.

Turning Red

The problem with mold is that it decays wood and, in large quantities, can pose health risks to people and animals. Rust, it turns out, kills mold and other types of fungi, so farmers began adding ferrous oxide (rusted iron) to the linseed oil mix. A little bit of rust went a long way in protecting the wood, and it gave the barn a nice red hue.

By the late 19th century, mass-produced paints made with chemical pigments became available to most people. Red was the least expensive color, so it remained the most popular for use on barns, except for a brief period when whitewash became cheaper and white barns started popping up. (White barns were also common on dairy farms in some parts of Pennsylvania, central Maryland, and the Shenandoah Valley, possibly because of the color's association with cleanliness and purity.)

Throughout Appalachia (a historically poorer region), many barns went unpainted for lack of money. In the tobacco regions of Kentucky and North Carolina, black and brown barns were the norm, since the dark colors helped heat the barn and cure tobacco.

Today, many barns are still painted the color traditionally used in a given region, with red still dominating the Northeast and Midwest.

Have you got a Big Question you'd like us to answer? If so, send it to bigquestions@mentalfloss.com.

This story was updated in 2019.

Is There An International Standard Governing Scientific Naming Conventions?

iStock/Grafissimo
iStock/Grafissimo

Jelle Zijlstra:

There are lots of different systems of scientific names with different conventions or rules governing them: chemicals, genes, stars, archeological cultures, and so on. But the one I'm familiar with is the naming system for animals.

The modern naming system for animals derives from the works of the 18th-century Swedish naturalist Carl von Linné (Latinized to Carolus Linnaeus). Linnaeus introduced the system of binominal nomenclature, where animals have names composed of two parts, like Homo sapiens. Linnaeus wrote in Latin and most his names were of Latin origin, although a few were derived from Greek, like Rhinoceros for rhinos, or from other languages, like Sus babyrussa for the babirusa (from Malay).

Other people also started using Linnaeus's system, and a system of rules was developed and eventually codified into what is now called the International Code of Zoological Nomenclature (ICZN). In this case, therefore, there is indeed an international standard governing naming conventions. However, it does not put very strict requirements on the derivation of names: they are merely required to be in the Latin alphabet.

In practice a lot of well-known scientific names are derived from Greek. This is especially true for genus names: Tyrannosaurus, Macropus (kangaroos), Drosophila (fruit flies), Caenorhabditis (nematode worms), Peromyscus (deermice), and so on. Species names are more likely to be derived from Latin (e.g., T. rex, C. elegans, P. maniculatus, but Drosophila melanogaster is Greek again).

One interesting pattern I've noticed in mammals is that even when Linnaeus named the first genus in a group by a Latin name, usually most later names for related genera use Greek roots instead. For example, Linnaeus gave the name Mus to mice, and that is still the genus name for the house mouse, but most related genera use compounds of the Greek-derived root -mys (from μῦς), which also means "mouse." Similarly, bats for Linnaeus were Vespertilio, but there are many more compounds of the Greek root -nycteris (νυκτερίς); pigs are Sus, but compounds usually use Greek -choerus (χοῖρος) or -hys/-hyus (ὗς); weasels are Mustela but compounds usually use -gale or -galea (γαλέη); horses are Equus but compounds use -hippus (ἵππος).

This post originally appeared on Quora. Click here to view.

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