I found this information on the Florida Department of Corrections website, so there is a lot of information that pertains to Florida, but it also contains some great information for parents that covers any location.   I have pulled some of that information and pasted it below and provided the full link in this post.
What are some typical pre-gang behaviors?
Gang involvement does not happen overnight. It is a gradual process and if you are alert you will see the signs.

  • Poor progress or achievement in school
  • Truancy from school
  • Lack of hobbies or too much leisure time
  • Frequent contact with authority figures or police
  • Draws gang insignias/symbols
  • Problems at home
  • Lives in neighborhood where gangs exist
  • Friends are gang members or “dressing down” or “sagging and bagging” in gang attire
  • Begins dressing in traditional gang clothes

How do you deal with gangs?
Be decisive, firm, and fair. Lenient treatment is viewed as weakness and they will take advantage of you.
Intimidation will not work; it will most likely lead to confrontation. Lectures do not work either. Gang members are looking for respect. Giving any public or media attention to a gang only feeds their egos and escalates gang activity. It is bad news to negotiate with terrorist or criminals, so don’t do it with gangs or their members–all it does is give them more recognition and power.

Remember the four “Rs” about graffiti–Read, Record, Report, Remove.
Prevent conflict whenever possible–look for common ground.

What can parents do?

  • Know your children’s friends.
  • Know about who and what influences your kids.
  • Know what your children are doing at all times.
  • Become involved with them and occupy their time.
  • Strive for good communication between you and your youngsters.
  • Again, spend time with them.
  • Do not allow gang dress.
  • Do not allow hanging in the streets or mall.
  • Be very suspicious of gang writing, graffiti, or tattoos.
  • Encourage anti-gang attitudes at home.
  • Learn about gangs and drugs.
  • Participate in your child’s education–find out what’s happening at school.
  • Get involved in community affairs.
  • Set the example for your kids–they will do what you do.
  • Believe in your young person.

What are some parental strategies to combat gangs?

  • More recreational and leisure-time activities for youngsters
  • A crack-down and tougher law enforcement against gang activities in the community
  • Stepped-up efforts to dry up the chief source of gang money–DRUGS
  • Increased parental supervision of children, their activities, and their friends
  • Collaborative efforts between police, community residents, and young people