Refrain from racial/ communal profiling. It is politically, legally and operationally wrong. Assuming that a given ethnic group/community has a higher potential for threat will result in ignorance of other ethnic groups that may very well be involved in the execution of a terrorist attack. What characterizes a terrorist is their choice of method and not their ethnic background. Engage suspicious activity using a customer service approach. The deterrence value of security and law enforcement is not in response to an authoritative voice or aggressiveness but to a carefully thought-through and targeted question as simple as: “how can I help you?” or “where are you heading?” These questions are regarded as service oriented to the law-abiding citizen but will be deterring to the terrorist, now confronting a situation where his false identity and terrorist intentions could be exposed. Attempting to refute suspicion instead of building a case. Often we are driven to jump to conclusions based on an observed suspicious activity. We assume threats or guilt even before engaging with the observed suspicion. Suspicion is a common occurrence that needs to be mitigated through refutation i.e. trying to prove the suspicion wrong and not validating it with an assumption of guilt.
(thanks to Chamelion)