The ever-relevant and intrusive Department of Homeland Security has released a pamphlet of guidelines, called "Identifying Homegrown Violent Extremists Before They Strike." Essentially it's, "How to Catch a Terrorist – Home Edition." No training required, just a keen eye and willingness to delve into the personal lives of your neighbors. The literature does not mention the word Muslim or Islam, and it features a black guy and a white guy, because terrorism, like undergraduate education, prides itself on ethnic diversity.
Here are a few of the provided "Indicators of Terrorist Activity:"
Adoption of a new life styles and segregation from normal peer and family groups in association with advocating criminal or terrorist activity.
Behavior that could indicate participation in surveillance of potential targets.
Travel to or interest in traveling overseas to attend violent extremist institutions or paramilitary training camps.
New or increased interest in Websites and reading materials that advocate violence and then initiating action in support of this activity.
With stuff like this, it's always hard to tell if it's well-intentioned and sensible, or silly fear-mongering. After all, if you strip out all the mentions of "violent activity," it sounds like a kid who moved across the country and likes to take photographs and read the news.