Yes, anyone who works with kids should be on the lookout for gang "signs" and "colors". Each locality has its own variation and there are "national" stuff. Here in New England, the Latin Kings are on the rise. They have elaborate hand signals. I don't pay attention to it because they are not yet recruiting in the Asian community. In the Lowell, some Hispanics with possible Latin king connections are in a miniwar with the Southeast Asian kids who have formed their own local gang. A fifteen year old Khmer kid was blown away just this past year on his front stoop. There has been a number of skirmishes not widely publicized outside of the community.
Here in Boston, some of the Asian Kids are being recruited, or emulating the Crips and the Bloods, wearing the respective colors of blue and red. Last year, at the Latin School (Boston's most prestigous high school) Asian Night cultural performances that was organized by some of my kids, several youth were beatened up and one stabbed seriously for wearing the wrong colors. There was a retaliation after that. In Allston/Brighton an Asian Kid wearing blue was seriously "dinked" by baseball bats by a group wearing red. Some in the red group were Asians as well. In nearby combat zone, I see southeast Asian kids, 10 - 15 at a time, sporting red. They venture into Chinatown once in awhile and tensions go way up, and there are occaisonal skirmishes.
Generally speaking, if you have a "gang" prescence in your dojo, it'll be more than one kid. Gangs are territorial (except in schools where they fight it out constantly). One gang will not let members of another gang onto their turf. Look for some conformity in dress, colors, hairstyles, tattoos, use of "signs". If see this, you would do well to investigate further. You can help kids who are not in "deep" yet to think it through. If they're in too deep, you may want to ask them to leave the dojo. To not do so is to risk other dojo members becoming possible, inadvertant recipients of stray bullets from a drive-by or a badly aimed "hit".
Sorry, this is the reality out there.