Graffiti art was popping up on sidewalks around England last week, advertising jobs at the Government Communications Headquarters, also known as the United Kingdom’s equivalent of the United States’ National Security Agency.

The spy agency confirmed with Fortune by email that the ads are legitimate. “The method is known as ‘clean graffiti,'” the agency’s press office said Thursday. “The ads were placed at the beginning of the week and are designed to fade over time.”

The classifieds read: “GCH-WHO? | TECHNICAL OPPORTUNITIES | GCHQ-CAREERS.CO.UK.”

James Cook, a tech reporter at Business Insider who spotted the ads last week in the London neighborhood of Shoreditch, noted that the careers website failed to load when he attempted to access it. “Forbidden,” the error page said, a bit ironically. “You do not have permission to access / on this server.” (The page now works.)

https://twitter.com/JamesLiamCook/status/665464768665403394

Victoria Turk, a UK-based editor at Vice Motherboard, initially speculated that the impediment might have been an intentional challenge designed for computer whizzes. “Knowing GCHQ’s previous attempts to recruit talent using codes and puzzles,” she writes, “I wondered if it was a secret test to weed out candidates who weren’t up to the task.”

According to GCHQ, she said, this was not so. It was a browser issue.

https://twitter.com/VickiTurk/status/664427047977140224

East London, where the ads appeared, is known for its high concentration of tech talent, which may explain the agency’s interest in targeting the neighborhood. The area has been branded “Silicon Roundabout.”

“We look at areas which are likely to contain a high proportion of people we would like to recruit,” the GCHQ press office told Fortune, “in this case people with technical skills and experience.”

Following the terror attacks in Paris on Friday, U.K. Prime Minister David Cameron said he plans to boost the country’s security spending, the Guardian reports. The extra investment will provide for a headcount bump of 1,900 intelligence and security officers in UK spy agencies, an increase of 15%.

Subversive street artists need not apply.

Follow Robert Hackett on Twitter at @rhhackett. Read his cybersecurity, technology, and business coverage here. And subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology, where he writes a weekly column.

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