The information found in the greeting cards is often used by members of the prison's Institutional Gang Investigative Unit as they collect evidence of prison-gang membership. The process, called "validation," includes searching cells for evidence, studying inmates' records for gang patterns in drug deals or fights, and even reading the inmates' mail.
"Say we're looking at somebody and trying to validate him," Clemons said. "We might find out who thought enough about him to send a card."
Condolence cards also are considered fair game for investigators. Clemons showed one which had been given to an inmate named Hannibal. On the outside was a fierce portrait of the historical Hannibal, clutching a black dagger inscribed with "RSC" -- for the Rollin' 60s Crips.
"Big U: Mr. Half Dead right here for you and the family," one message inside the card said. "I'll always keep you and your little brother in my prayers. Please keep a cool head Big Homie."
To Preciado and Clemons, the cards are full of arcane signs that an outsider might easily miss. Clemons pointed to a tiny detail on one card with a muscled Aztec warrior on the cover. Hidden in the clothing patterns was the word "Eme," Spanish for the letter M and a reference to the Mexican Mafia.
Another card shows a young man in a wizard's hat holding a set of keys: a sign that the recipient is a "llavero" -- the shot-caller who "holds the keys" to big decisions in the yard.
About three years ago, investigators confirmed that the recipient of the card, Evaristo Garnica, a former member of Los Angeles' Cypress Park street gang, was an associate of the Mexican Mafia, Clemons said. Garnica is currently in the special housing unit at Pelican Bay.
Preciado said he was not surprised that inmates sometimes leave obvious signs of gang activity.
"A lot of these guys can't let it go," Preciado said. "They're making thousands of dollars" -- by controlling the sale of drugs and other contraband -- "and they don't want to give up that money. It's all about the power and the money."
For those inmates with a knack for drawing, the production of prison greeting cards is a more modest way to earn some extra cash. Lancaster inmate Joseph Marquez learned the prison-art aesthetic from his incarcerated father. The 33-year-old, who is serving seven years for robbery, said he can make about $3 for drawing a simple birthday card, and as much as $10 for one with a complex collage.
The finished product is usually passed around the cellblock, then presented to the birthday inmate with a spread of snacks from the commissary and, usually, a fresh batch of pruno. Sometimes, prison officials say, inmates will chip in for a dose of heroin, currently the favored intoxicant among those California convicts who use drugs.
But Marquez says it is the cards that make an inmate feel that life, for a moment, is almost normal again.
"A card makes a big difference," he said. "It makes a guy feel a lot better."