In case decapitating their victims and dumping the heads in picnic coolers didn't make the point, the killers left a note.
"This is a warning," it said, listing an alphabet soup of Mexican police agencies and the noms de guerre of several well-known drug figures. "You get what you deserve."
The message, scrawled on a poster in black ink, accompanied four severed human heads that Mexican authorities recently found on a highway in the northern state of Durango.
The same day, police in neighboring Chihuahua state came upon five swaddled bodies accompanied by a hand- lettered placard.
"This is what happens to stupid traitors who take sides with Chapo Guzman," said the message found in Ciudad Juarez, referring to Joaquin "Shorty" Guzman, the supposed leader of the main drug gang in adjacent Sinaloa state.
The killers closed with incongruous propriety: "Yours truly," they signed off, "La Linea."
Amid a wave of drug-related violence across Mexico, the dead these days are frequently accompanied by macabre calling cards known popularly as "narco-messages."
Part threat and part boast, the messages have multiplied as drug killings have risen to record levels amid a government crackdown on organized crime and deadly turf wars among traffickers.
Written by hand and often with grammatical errors, the notes are frequently publicized in Mexican news reports and on the Internet, allowing drug gangs to deliver their fearsome messages to enemies and society at large. The messages can even serve as a conversation between rivals.
Five days after police in Durango discovered the severed heads, they found another head, also with a message. It was an apparent answer to the earlier killings.
"We too can respond," the note said, according to Mexican news reports.
Analysts and law enforcement officials view the messages as a version of wartime psychological operations, lending medieval-style brutality a touch of 21st century media savvy.
"I'm the boss of this turf," read a banner in Sinaloa bearing the name of Arturo Beltran, whose faction is battling Guzman's. "And this is the beginning."
Grisly death has long been part of Mexico's illicit drug trade. But the frequency and brazenness of the narco-messages, including videos and photos of executions posted on YouTube, are a further sign that the violence has grown more savage.
"You didn't see that kind of stuff 13 years ago," said a senior U.S. counter-narcotics official. "It's more in-your-face."
Such was the case in Tijuana in April when rival factions of the Arellano Felix drug gang engaged in a wild gun battle that left 13 gunmen dead.
One of the bodies that turned up bore three words written on the skin in marker: "Traidor, Enemigo, Objetivo," or "Traitor, Enemy, Target." The first letters of the three Spanish words spelled "Teo," the nickname of Teodoro Garcia Simental, leader of one of the warring factions.
In Sinaloa state, site of a violent conflict between Guzman and former allies led by Beltran, white cloth banners have been lashed to overpasses and billboards. The messages, lettered in black and red, are peppered with the nicknames of key players and frequently too arcane to follow.
Often, government forces are the target audience. A recent poster mocked army troops on patrol, calling them "little lead soldiers."
In the border cities of Nuevo Laredo and Reynosa, in the state of Tamaulipas, neatly painted banners appeared this spring advertising jobs in the Zetas, one of the country's most fearsome crime groups.
The banners, addressed to "soldiers or ex-soldiers," offered "good wages, food and help for your family."
It is unclear whether the banners were a genuine recruitment effort by the Zetas, the armed wing of the so-called Gulf cartel, which operates along the Texas border. But many Nuevo Laredo residents remain convinced that the offer was real, underlining the degree to which Mexicans stand in awe of the reach of drug trafficking organizations.
"It does little good that the armed forces have more firepower than the drug traffickers if the federal government adopts a passive attitude before the psychological operations of organized crime," columnist Jorge Luis Sierra wrote in El Universal newspaper.
Many residents of Ciudad Juarez stayed indoors on a recent weekend after a widely circulated e-mail warned that the city was about to endure its "bloodiest" weekend yet.
It is unknown whether the threat was real: Authorities reported 17 people dead around Ciudad Juarez in separate incidents over three days, a rate not out of line with the norm since the killings surged early this year.
Ciudad Juarez residents have reason to take anonymous warnings seriously. In January, someone threatened city police by posting the names of 17 officers on a monument to fallen officers. Three of those listed were already dead.
By mid-May, about half of those listed had been killed, including the city's No. 2 police official, who was peppered with automatic-weapons fire one night as he returned home.
The messages keep on coming. Late last month, two hand-scrawled banners appeared in the Chihuahua state capital, also called Chihuahua. Signed by a group calling itself Gente Nueva, or New People, the banners listed the names of 21 state police officers.
The threat needed no elaboration.