I found the below on the Los Angeles Police Department website. It is not real specific but I think it provides some good highlights on warnings that parents can look for in their kid’s clothing.
“Clothing. The uniform of Hispanic gangs is standard and easily recognizable. Most gang members adopt a basic style that includes white T-shirts, thin belts, baggy pants with split cuffs, a black or blue knit cap (beanie) or a bandana tied around the forehead similar to a sweat band.
Black gang members are individualistic in their dress. Black gangs tend to identify themselves by adopting certain colors. The “Crips” identify themselves with the colors of blue or black or a combination of the two. “Blood” gangs generally use red accessories, such as caps or bandanas, to identify themselves.
While clothing alone cannot positively determine membership in a street gang, color and style serve to identify each gang. Green can either mean the gang member is declaring neutrality for the moment or is a drug dealer. Black is worn by some Hispanic gangs and Heavy Metal Anglo gangs. Other common gang colors include brown or purple.
Note: Some gangs are starting to change their clothing style by no longer wearing their colors in an effort to deceive law enforcement and conceal their gang affiliation.
Gang clothing styles can be easily detected because of the specific way gang members wear their clothing. Examples are preferences for wearing baggy or “sagging” pants or having baseball caps turned at an angle. Gang members often prefer particular brands of shoes, pants or shirts. For example, some gangs like to wear plaid shirts in either blue, brown, black or red. These shirts are worn loosely and untucked. Gang graffiti, symbols, messages or gang names can be written or embroidered on jackets, pants and baseball caps. Other identifying items include belt buckles with the gangs initials, key chains, starter jackets (team jackets), and red or blue bandannas commonly called “rags”.
Excessive amounts of dark clothing or a predominance of one-color outfits, white T-shirts and levis with upturned cuffs are also indicators of possible gang involvement.
Jewelry. May be expensive or cheap, but the gaudy type is preferred. Examples are heavy gold rope chains, earrings and other large rings.”