Tattoos are more common in the workplace than ever before, but they can still be an occupational hazard. Particularly when your profession happens to be spy.

Spycraft often involves moving between legal and criminal worlds—and few things are as risky as being discovered while gathering intelligence. Common sense dictates that for spies, ink would serve as a means of easy recognition. Tattoos, after all, have long been used to determine identity, from verifying allegiances to specific gangs to providing clues in forensic investigations.

The identification of criminals has often hinged on distinguishing marks, from mundane burglars to famous perps like the Chicago mass murderer Richard Speck. When Speck was rushed to Cook County Hospital after a suicide attempt on July 17, 1966, he was recognized by a doctor who had seen his “Born to Raise Hell” tattoo publicized in the newspaper.

Criminals have even been outed by the absence of crucial tattoos. In a famous 19th-century legal case, Australian national Arthur Orton reinvented himself as shipwreck victim Roger Tichborne, heir to a family fortune. Orton was revealed as an imposter, in part, due to his lack of certain tattoos that Tichborne was known to have worn.

A gruesome account of the consequences of being a tattooed spy comes from the 17th-century travel account of Scotsman William Lithgow. In his memoir, Lithgow tells the tale of being captured in Málaga, Spain, in 1620, where the governor  “swearing, cursed and said, ‘thou leyest like a Villane, thou art a spy and a traytor,’” and accused Lithgow of providing intelligence learned in Spain to a visiting English ship.  (The memoir wisely does not confirm if Lithgow was indeed spying). He was imprisoned and tortured at the hands of Spanish inquisitors, who tried to force a confession.

Part of Lithgow’s torture involved having a tattoo flayed from his skin. He had received this tattoo—a royal crown commemorating King James I of England—while traveling in the Holy Land. His cringe-worthy account begins: “The Corrigidor…gave direction, to teare a sunder, the name, and Crowne (as hee sayd) of that Hereticke King, and arch-enemy to the Holy Catholicke Church.”

Lithgow then proceeded to relate a method by which taut cords were used to excise a chunk of flesh out of his arm to remove the offensive mark “cutting the Crowne, sinewes and flesh to the bare bones.” Lithgow’s arm would be damaged for the rest of his life.

With regard to more contemporary intelligence history, representatives from various government agencies remain necessarily vague about their stance on tattoos, so as not to jeopardize any investigations or compromise agents. But tattoos aren’t necessarily banned for agents. As Nicole de Haay, a CIA spokesperson puts it: “Despite what you may have heard, the CIA employs individuals with tattoos, as our workforce is as diverse as the nation that we protect.”

One FBI representative, who requested anonymity, disclosed that “tattoos are not prohibited in undercover work in the FBI,” but acknowledged that such markings “could present as a potential risk to the undercover operation and the employee especially.”

Across the Atlantic Ocean, a spokesperson for the United Kingdom’s Home Office explained that due to reasons of national security they could never comment on operational matters of MI5. However, he left open the possibility that tattoos might be allowable in some situations while conceding they would not be appropriate for other jobs.

In certain cases, tattoos even can be beneficial in crafting an identity as a spy. Jay Dobyns, a former agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), found his tattoos actually helped him to go undercover. Dobyns already had half-sleeve tattoos when he was selected by the ATF to lead a two-year undercover investigation into the Hells Angels biker gang in 2002.

Although tattoos were not a requirement for assignment to the “Operation Black Biscuit” team, Dobyns notes they helped him assimilate. “My undercover persona would not have changed without the tattoos,” he says, “but my story, coupled with my appearance, made me believable.” Dobyns even continued to get tattooed while undercover; Hells Angels tattooers inscribed angels and flames on his arms.

Dobyns took one precaution to avoid raising suspicion. One of his previous tattoos had the date “February 28, 1993” included as part of a design honoring fellow agents killed in the Waco siege. He had the date covered, he says, “because my suspects were very clever and observant, and I did not want to create a question for myself that I did not have a solid or believable answer to. I didn’t want to have to lie on top of my lie.”

Beyond signifying their wearer’s affiliation with a group, tattoos have been used to send encrypted messages in a more literal sense. Onscreen, body art has encoded cryptic information, as in the film Memento and the television show Prison Break. But the practice is a lot older than that. One of the earliest uses of steganography (hiding messages within other messages) is documented in the writings of Herodotus from 440 BC.

In The Histories, Herodotus writes that Histiaeus, the tyrant of Miletus, grew tired of living abroad in service to King Darius of Persia. Longing to return home, “he shaved and tattooed the head of his most trustworthy slave” with a secret message asking his nephew and son-in-law Aristagoras, who was ruling in his place, to stage a “revolt from the king,” so that Histiaeus would be sent to quell it.

When the messenger arrived in Miletus, he told Aristagoras to “shave his hair and examine his head,” thus revealing the plan. As a result of the staged revolt, Darius allowed Histiaeus to leave Susa, though his plan to return to ruling Miletus ultimately failed.

Official confirmation of the roles tattoos have played in later spy operations can be harder to come by, but the art form’s potential utility is undeniable. In the 21st century, innovations in tattoo removal and lightening techniques have made tattoos easier to cover with new inked designs.

No longer do spies have to fear being outed for their tattoos after an undercover assignment—they can radically change the designs or erase them altogether. Who knows what clever new uses tattoos may have been put to already, hidden away in classified files for future historians to discover?