Their tattoos, specifically, according to this piece in Motherboard. The FBI teamed up with the National Institute for Standards and Technology to create a database for software that identifies people – and (the key part) profiles them – by their tattoos:
One slide from an NIST presentation titled “Why Tattoos?” makes clear how law enforcement would use the system, which was developed alongside a group of third-party companies, universities, and private research institutions, to profile people en-masse. The slide explicitly states that tattoos “suggest affiliation to gangs, subcultures, religious or ritualistic beliefs, or political ideology” and “contain intelligence; messages, meaning and motivation.”
What’s more, the government researchers failed to disclose that 15,000 tattoo images used in the initial experiment, called “Tatt-C,” came from prisoners who had not consented to the experiment—apparently in violation of federal rules for ethical research.
The use of prisoners in scientific research comes with a number of caveats to protect inmates from exploitation. Specifically, the rules limit the kinds of experiments that can be performed and require oversight by an independent review board that must include representation from at least one inmate.
But according to the documents obtained by the EFF, the researchers failed to disclose the experiment’s use of prisoners, initially saying only that the data was “operationally collected.” NIST higher-ups only approved the experiment retroactively, under the impression that it didn’t involve data from human subjects at all.
The data was also distributed to 19 different third party companies and organizations, including MorphoTrak, a massive biometric technology firm that has done business with various US agencies.
So… if you’ve been inked using the same premade flash as, I dunno, some artist who’s done the Florida Outlaws or something, you could be pinging a database. “This one. Look at this one.”