Tips for spotting suspicious activities

(CNN) -- U.S. Attorney General John Ashcroft has told Americans to keep alert in the aftermath of the September 11 terrorist attacks and report anything suspicious to law enforcement agencies, with a "heightened sense of awareness."

But a definition of suspicious behavior is difficult to establish, because there is no "cookie-cutter" behavior for terrorist activity, said Thomas Sweeney, co-chair of the private sector liaison committee for the International Association of Chiefs of Police, a group exploring the boundaries between private security and law enforcement, in order to improve security on both sides.

However, there are several things to look for, added Sweeney, who is also the police chief in Glastonbury, Connecticut. It's better to spot things at the level of suspicion, before they become an incident, he said.

Be sensitive to your environment.

Watch for:

1. Someone attempting to gain access to something they shouldn't have or somewhere they don't belong.
Examples include getting near chemicals, vehicles or buildings without proper credentials, Sweeney said.

2. Strange or frequent comings or goings

3. Someone carrying a weapon
People should already be notifying police if they notice unauthorized people carrying weapons or using them threateningly, Sweeney said.

4. Someone who appears to be concealing something or attempting to put something over on somebody

5. Clues on the job
Sweeney says some crime solving has come from tips by people at work -- for example, film processing or computer-repair employees who noticed something out of the ordinary.

6. Suspicious mail or packages (Read the tips)

7. Watch for people conducting themselves in a strange manner or making unusual requests
Example: The case of a student pilot interested only in learning how to steer a plane, not take off or land. Sweeney said it might be something that strikes you as not appropriate for whatever environment you're operating in, or something that just seems abnormal.

If you notice something suspicious, call 911, or the local police department.

Police officers across the country are experiencing increased calls reporting incidents of suspicious people and packages, Sweeney said, which is exactly what he wants to see. "It's better to report than to speculate," he said. All police departments have the information to refer each type of incident to the appropriate agency.

Remain calm, without overreacting

Some law officials have expressed frustration that well-intentioned citizens, frightened by the most innocent of circumstances, have stretched their workforce thin. A rider ordered a bus stopped and evacuated because sand on the floor was feared to be a suspicious powder. A cardboard box on a curb was assumed to be a bomb. A truck that kicked up a cloud of dust was thought to be men of Middle Eastern descent spraying the road.

"We had 80 calls of suspicious substances or packages yesterday," said one official. "Not one of them produced anything at all."