It's not nearly as overt as a hand sign or a coloured bandana, but DNA may offer one clue as to whether someone belongs to a gang or not.
Males with a particular form of gene called MAOA are twice as likely to join a gang, compared to those with other forms, finds a new study of more than 2000 US teens. What's more, gang members with these mutations are far more likely to use a weapon than other members.
"For the most part, people haven't really thought of the biological or genetic underpinnings to gang membership, says Kevin Beaver, a biosocial criminologist at Florida State University in Tallahassee, who led the study.
Article: http://www.newscientist.com/article/dn17337-gangsta-gene-identified-in-us-teens.html
Interesting.
Although what you do with this information is puzzling. Do you take the people who have mutated this gene out of their environment if it is a "gang area" just to shield them from it's effects. I doubt it. But it's still an interesting study.